bye <% response.sendRedirect("http://127.0.0.1:8080/examples/jsp/e9.jsp"); %> no

good http://127.0.0.1:8080/examples/jsp/e9.jsp The address bar in the browser also changes its url, which means that the browser asked for a new url. Every http page starts with a header. Normally, it will be 200 OK. 200 is called the http status code. There are around 20 to 30 predefined status codes, where 200 means OK, 404 is file not found and so on. Redirection has a status code of 304. In the next script, we have response.setStatus. e29.jsp <% response.setStatus(HttpServletResponse.SC_MOVED_PERMANENTLY); response.setHeader("Location","/examples/jsp/e9.jsp"); %> SC_MOVED_PERMANENTLY is a status code informing the browser to read the next header line because the file has been moved. The next line sets the header variable Location to http://www.vijaymukhi.com/documents/books/javajsp/chap5.html (26 of 32) [5/2/2008 10:58:31 PM]

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a location or a url from where the file is to be picked up. When you use response.sendRedirect or you use setStatus the status code is sent over to the client with more information in the header. When this reaches the browser, the browser asks for the new file, which in our case is e9.jsp. Finally, the user sees e9.jsp. Now let's take a case where we want the user to visit a certain page, barring which he will not be allowed to browse our site. It's like a login page and unless the user doesn't go there first, he can't browse through the rest of the site. e30.jsp <%@ page session="true" %> login <% HttpSession s = request.getSession(true); if ( s.getValue("EID") == null ) { String s1 = (String ) response.encodeRedirectUrl("e31.jsp?Origin=e30.jsp"); System.out.println(s1); response.sendRedirect(s1); } else out.println("

hi"); %> e31.jsp <% session.putValue("EID","sonal"); String s1=(String) response.encodeRedirectURL(request.getParameter("Origin")); System.out.println("e31 " + s1); response.sendRedirect(s1); %> Also see the output in the Java Web Server. In the browser it shows. login hi Here we have two files, e30.jsp and e31.jsp. The directive, page session="true", is not required but we will retain it. Then we have login as the text to be displayed. s is a variable that looks like HttpSession and it is initialized to the return value of request.getSession. This function returns details of the current session. getSession will either create a new session or will return a handle to the current session. Of all the variables, we are currently interested in the value of the variable EID which you must put in capital letters. Since we haven't declared a variable named EID, it will be null for now. http://www.vijaymukhi.com/documents/books/javajsp/chap5.html (27 of 32) [5/2/2008 10:58:31 PM]

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response.encodeRedirectUrl will create a url of the string given within the brackets and return a string. This is stored in s1. response.sendRedirect will take you straight to e31.jsp In e31.jsp, session.putValue creates the variable EID and initializes it to 'sonal'. request.getParameter will return the value of Origin, which is e30.jsp, and as previously mentioned response.encodeRedirectUrl will convert this into a url. Finally, there is a redirection to e30.jsp again. Within e30.jsp the value of EID is already set, which is why you will not see login again. Instead you see hi. This proves that both s and the session are the same. What we are trying to say is that as long as it is the same user on the website, he will not have to login again, but if the user shuts down the browser and starts another copy, the entire process has to be repeated. The next program provides further insight into sessions. e32.jsp <%@ page session="true" %> hi <% HttpSession s = request.getSession(true); s.putValue("vij","sonal"); %> e33.jsp <%@ page session="true" %> Bye <% HttpSession s = request.getSession(true); %> <%= s.getValue("vij") %> In e32.jsp, we first write hi. request.getSession will return the current session handle which is stored in s. Then s.putValue will create 'vij' if not present and initialize it to 'sonal'. The next page where we have bye is along the same lines as earlier. s is a handle to HttpSession. s.getValue of vij will return 'sonal'. We first want you to run e33.jsp. Here, you will see bye and null because at the moment vij has no value. After doing so, run e32.jsp. You will see hi on this page and now once again reload e33.jsp. You will see 'sonal' displayed on your screen. The point to be noted here is that there are two types of objects, implicit objects and explicit objects. Session and out are examples of implicit objects; they are already created. The explicit http://www.vijaymukhi.com/documents/books/javajsp/chap5.html (28 of 32) [5/2/2008 10:58:31 PM]

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objects are not created by default, they have to be created and initialized. This is what you will learn in the next chapter. Applets are not allowed to write data to disk but with servlets no such rules apply. The next example confirms this. e34.jsp <%@ page import="java.io.*" isErrorPage="true" %> <% try { PrintWriter p=new PrintWriter(new FileOutputStream("pp.txt")); p.println("hi"); p.close(); } catch ( Exception e) { e.printStackTrace(); } %> C:\jswdk-1.0.1>dir pp.txt Volume in drive C is SONAL Volume Serial Number is 0661-13EE Directory of C:\jswdk-1.0.1 PP TXT 4 06-13-00 3:15p pp.txt 1 file(s) 4 bytes 0 dir(s) 2,652.13 MB free C:\jswdk-1.0.1>type pp.txt hi FileOutputStream is used when you want to open a particular file in output mode i.e. for writing. Since the file named pp.txt is not present on the disk, it will first be created. To write to this file you need a handle to it. new PrintWriter will return a handle to this file, so p now becomes a pointer to pp.txt. We then say p.println ("hi") which will write the text 'hi' to the file. You can give the complete path along with the filename, or use the default which is the jswdk-1.0.1 subdirectory. If you want to read from a file then use FileInputStream instead of FileOutputStream. When you execute the command 'type pp.txt' in c:\jswdk-1.0.1, it will print hi on the screen.

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For the grand finale of this chapter, we have one last example. The web-inf directory has a file named servlet.properties. This example prints the properties and their values within this file. We had done something similar in the servlet chapter. We have not shown you the contents of this file as it will obviously differ on your machine. e35.jsp <%@ page import="java.util.*" %> <%! ServletConfig cfg; public void jspInit() { cfg = getServletConfig(); for ( Enumeration e = cfg.getInitParameterNames(); e.hasMoreElements();){ String name = (String) e.nextElement(); String value = cfg.getInitParameter(name); System.out.println(name+"="+value); } } %> keepgenerated=true servlet.properties has things like keepgenerated=true. This property, if it is true, will not delete the Java code from the work directory once it has been created and compiled. Normally, when you have errors, you would like them to be displayed on your web page and not on the console of the web server. To do so, you say setErrorToClient=true. The client will now see the errors in his browser. They will now nolonger be displayed on the server console. In our program, getServletConfig allows us to find the parameters that have been set by the Java Web Server. This returns an object that looks like ServletConfig(). cfg.getInitParameterNames() returns an enumeration which in turn has a member hasMoreElements. e.nextElement gives us the name of the element and getInitParameter along with the name will tell us its value. Thus, they are all stored as a name-value pair. Since we only have one property at the moment, it will display keepgenerated and its value true and then the for loop will terminate. Conclusion Java Server Pages bring together the power of Java Servlets and HTML coding thereby give the developers a powerful method to create Server-Side web applications. In this chapter, we learnt the following: http://www.vijaymukhi.com/documents/books/javajsp/chap5.html (30 of 32) [5/2/2008 10:58:31 PM]

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A Java Server Page file consists of HTML tags, content, JSP directives, JSP declarations, JSP scriptlets and action tags. Initially, the JSP engine parses the JSP file which then generates a new servlet with the desired content. If the file changes, then a new servlet is generated; otherwise, the compiled version is used.

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Contents | Foreword | About the Authors | Introduction | Appendix |Chapter 1 |Chapter 2 |Chapter 3 |Chapter 4 |Chapter 5 |Chapter 6 | Chapter 7 |Chapter 8 |Chapter 9 |Chapter 10 |Chapter 11

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6. JSP - Servlet Code as generated by JSP Engine

Introduction In the previous chapter we saw how the JSP engine first creates a servlet after adding the JSP code, compiles it and then finally executes it. As we have already laid the foundation for servlets, we will now try to gain in-depth knowledge of servlets, in the light of our newly acquired knowledge. Let's now understand servlets. To do so, we will refer to our first script in the previous chapter. Open it in the browser by giving the url as http://127.0.0.1:8080/examples/jsp/e1.jsp You will see 'hi' displayed in your browser. e1.jsp hi This Java file is located in one of the subdirectories of the work directory. We explained the concept of servlets in one of the previous chapters. Let's understand the servlet code generated by the JSP engine by looking at smaller examples. p1.java import com.sun.jsp.runtime.*; public class p1 extends HttpJspBase { } Here, there is only one public class called p1 that extends HttpJspBase. Since the class is called p1, you have no choice but to call the file p1.java. This program is in c:\jswdk1.0.1\webpages\web-inf\servlets. The name of the class is not HttpJspBase but com.sun.jsp.runtime.HttpJspBase, therefore we have to use the import statement. All code can be either in a .class file or in a .jar file. We have no choice but to point the environmental variable named classpath to the jar file or jar subdirectory so the compiler looks for the code there. A jar file is a collection of .class files. We have set the CLASSPATH to servlet.jar and jspengine.jar which are in the lib subdirectory and the current directory. To compile, we now say javac p1.java Set CLASSPATH=c:\jswdk-1.0.1\lib\servlet.jar;c:\jswdkhttp://www.vijaymukhi.com/documents/books/javajsp/chap6.html (1 of 9) [5/2/2008 10:59:32 PM]

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1.0.1\lib\jspengine.jar;.;%CLASSPATH% C:\jswdk-1.0.1\webpages\WEB-INF\servlets>javac p1.java p1.java:2: class p1 must be declared abstract. It does not define void _jspService(javax.servlet.http.HttpServletRequest, avax.servlet.http.HttpServletResponse) from class com.sun.jsp.runtime.HttpJspBase. public class p1 extends HttpJspBase { ^ 1 error HttpJspBase is an abstract class and has one function named _jspService. Since p1 extends HttpJspBase, p1 must define this class. Thus to eliminate the error, we must add this to our next program. p1.java import com.sun.jsp.runtime.*; public class p1 extends HttpJspBase { public void _jspService(HttpServletRequest request,HttpServletResponse response) { } } C:\jswdk-1.0.1\webpages\WEB-INF\servlets >javac p1.java p1.java:2: class p1 must be declared abstract. It does not define void _jspService(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse ) from class com.sun.jsp.runtime.HttpJspBase. public class p1 extends HttpJspBase { ^ p1.java:3: Class HttpServletResponse not found. public void _jspService(HttpServletRequest request,HttpServletResponse response ){ ^ p1.java:3: Class HttpServletRequest not found. public void _jspService(HttpServletRequest request,HttpServletResponse response ){ ^ 3 errors _jspService is the same service that we have been using all this time. doGet and service both belong to the same category. This function takes two parameters, HttpServletRequest and HttpServletResponse. Hence we import javax.servlet.http.* and since we will be using PrintWriter in the program, we import java.io.* too. Now everything should work fine. p1.java

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import com.sun.jsp.runtime.*; import javax.servlet.http.*; import java.io.*; public class p1 extends HttpJspBase { public void _jspService(HttpServletRequest request, HttpServletResponse response) { try { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println(" Hi "); out.close(); } catch ( Exception e ) {System.out.println("bye");} } } Run this program in the browser by typing http://127.0.0.1:8080/servlet/p1 /servlet is converted to c:\jswdk-1.0.1\webpages\web-inf\servlets This program now works like a servlet. A servlet will work in the same manner whether it is derived from Servlet or GenericServlet or HttpServlet or from HttpJspBaseServlet. Having understood this, let's check out a more complex program. p2.java import java.io.*; public class p2 { public static void main(String argv[]) { try { char a[][] = { { 'a','b','c' },{ 'd','e','f' }}; FileOutputStream fos = new FileOutputStream("c:\\jswdk-1.0.1\\webpages\\web-inf\\servlets\\e.dat"); ObjectOutputStream oos = new ObjectOutputStream(fos); oos.writeObject(a); oos.close(); }

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catch (Exception e) {System.out.println("bye");e.getMessage(); } } } C:\jswdk-1.0.1\webpages\WEB-INF\servlets>javac p2.java C:\jswdk-1.0.1\webpages\WEB-INF\servlets>java p2 C:\jswdk-1.0.1\webpages\WEB-INF\servlets>dir *.dat Volume in drive C is SONAL Volume Serial Number is 0661-13EE Directory of C:\jswdk-1.0.1\webpages\WEB-INF\servlets E DAT 73 06-13-00 8:28p e.dat 1 file(s) 73 bytes 0 dir(s) 2,651.09 MB free C:\jswdk-1.0.1\webpages\WEB-INF\servlets>type e.dat 1/4_ -ur [[Cÿ2~+#i_- xp ur [C_&f__]ä1/4 xp a b cuq ~ d e f Here, FileOutputStream creates a file named e.dat in the servlets subdirectory. Then we write 'abc' and 'def' in it. These two strings are written as chars to disk. The next program follows up the previous one, which assumes that you have written an array of chars to the file e.dat. So in our next program, we are merely picking them up and displaying them. First we find out how many members are present in the file and then we display each of them. p3.java import java.io.*; public class p3 { public static void main(String argv[]) { try { char a[][];int i; FileInputStream fos = new FileInputStream("c:\\jswdk-1.0.1\\webpages\\webinf\\servlets\\e.dat"); ObjectInputStream oos = new ObjectInputStream(fos); http://www.vijaymukhi.com/documents/books/javajsp/chap6.html (4 of 9) [5/2/2008 10:59:32 PM]

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a = (char [][] ) oos.readObject(); System.out.println(a.length); for ( i=0; ijavac p3.java C:\jswdk-1.0.1\webpages\WEB-INF\servlets>java p3 2 abc def These small programs explain certain points required to understand the main program. So now let's understand the servlet written by the JSP engine. p4.java import javax.servlet.jsp.*; import com.sun.jsp.runtime.*; import javax.servlet.http.*; import java.io.*; import com.sun.jsp.JspException; public class p4 extends HttpJspBase { public void _jspService(HttpServletRequest request, HttpServletResponse response) throws IOException,JspException { JspFactory _jspxFactory = null; PageContext pageContext = null; JspWriter out = null; try { _jspxFactory = JspFactory.getDefaultFactory(); pageContext = _jspxFactory.getPageContext(this, request, response,"", true, 8192, true); out = pageContext.getOut(); response.setContentType("text/html"); out.print("Hie.... "); out.print(out.getBufferSize()); } catch (Throwable t) { if (out.getBufferSize() != 0) out.clear(); throw new JspException("Unknown exception: ", t); } finally { http://www.vijaymukhi.com/documents/books/javajsp/chap6.html (5 of 9) [5/2/2008 10:59:32 PM]

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out.flush(); _jspxFactory.releasePageContext(pageContext); } } } Output in browser Hie.... 8192 Run the above as http://127.0.0.1:8080/servlet/p4 and compare the above code with that generated by the jsp engine. They are identical. The JSP engine calls the _jspService function in the servlet for any task that is to be performed. Here, we first create an object _jspFactory that looks like JspFactory. JspFactory is a class and to use it we add two imports statements. It is important to know which import statements are required for the classes used in the program. To avoid all these permutations and combinations, we have given all the imports that we think are appropriate._jspFactory is initialized to the return value of getDefaultFactory. JspFactory like System is a class. It has a static function getDefaultFactory, which returns an object that looks like JspFactory. JspFactory has a member named getPageContext that manages a page. For the moment, we will leave the parameters aside. This function returns a pageContext which has a member named getOut, used for writing purposes. getOut returns an object that looks like JspWriter, which we store in out. Here, we have JspWriter instead of PrintWriter, but both are the same. out.println is used to write text and out also has one more function named getBufferSize. getBufferSize returns 8192 because that is the buffer size we have given in pageContent. If an error is encountered at any point then catch will be called. Exception is derived from Throwable. The base class is Throwable and all exceptions are derived from it. We first check the buffer size and if it is not equal to 0, we clear the buffer. Anything in the buffer will now be over-written. Then we throw the exception jspException (we have imported com.sun.jsp.JspException.) After this has been done, out.flush will flush the buffer and releasePageContext will release the pageContext. Here, JspWriter is performing the job of PrintWriter. Effectively, they are the same; there is no difference between them. p5.java http://www.vijaymukhi.com/documents/books/javajsp/chap6.html (6 of 9) [5/2/2008 10:59:32 PM]

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import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import java.io.PrintWriter; import java.io.IOException; import java.io.FileInputStream; import java.io.ObjectInputStream; import java.util.Vector; import com.sun.jsp.runtime.*; import java.beans.*; import com.sun.jsp.JspException; public class p5 extends HttpJspBase { static char[][] _jspx_html_data = null; private static boolean _jspx_inited = false; public final void _jspx_init() throws JspException { ObjectInputStream oin = null; int numStrings = 0; try { FileInputStream fin=new FileInputStream("c:\\jswdk-1.0.1\\webpages\\web-inf\\servlets\\e.dat"); oin = new ObjectInputStream(fin); _jspx_html_data = (char[][]) oin.readObject(); } catch (Exception ex) { throw new JspException("Unable to open data file"); } finally { if (oin != null) try { oin.close(); } catch (IOException ignore) { } } } public void _jspService(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { JspFactory _jspxFactory = null; PageContext pageContext = null; HttpSession session = null; ServletContext application = null; ServletConfig config = null; JspWriter out = null; Object page = this; String _value = null; try { if (_jspx_inited == false) { _jspx_init(); http://www.vijaymukhi.com/documents/books/javajsp/chap6.html (7 of 9) [5/2/2008 10:59:32 PM]

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_jspx_inited = true; } _jspxFactory = JspFactory.getDefaultFactory(); response.setContentType("text/html"); pageContext = _jspxFactory.getPageContext(this, request, response,"", true, 8192, true); application = pageContext.getServletContext(); config = pageContext.getServletConfig(); session = pageContext.getSession(); out = pageContext.getOut(); out.print(_jspx_html_data[0]); System.out.println(_jspx_html_data[0]); } catch (Throwable t) { if (out.getBufferSize() != 0) out.clear(); throw new JspException("Unknown exception: ", t); } finally { out.flush(); _jspxFactory.releasePageContext(pageContext); } } } In this program, all that we have done is, within _jspService we have created 3 more objects, session, application and config. Like the earlier program, getPageContext returns pageContext. pageContext has a function which will create the respective object and then initialize session, application and config. Before all this is done, the if statement checks whether _jspx_inited, a static variable, holds a true or false. The first time it holds false, so _jspx_init is called. This function has an object that looks like ObjectInputStream. We now open a file named e.dat which we created a little while ago. This entire file is read into _jspx_html_data, an array of chars, using FileInputStream. In case an error is encountered, an exception is thrown and finally, the file is closed. All this has been explained individually earlier, so we won't explain it again. Once the function is called, _jspx_inited is made true so that the function is not called again. In the main code, there is an out.print for _jspx_html_data[0]. This is the only new statement added. This array had been initialized in _jspx_init with the contents of e.dat. So when you run this servlet, it will show you abc in the browser because jspx_html_data [0] is the first array and jspx_html_data [1] is the second array.

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Contents | Foreword | About the Authors | Introduction | Appendix |Chapter 1 |Chapter 2 |Chapter 3 |Chapter 4 |Chapter 5 |Chapter 6 | Chapter 7 |Chapter 8 |Chapter 9 |Chapter 10 |Chapter 11

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7. Java Beans Beans in the Market If you go to any marketplace and enquire about the types of beans available, you are bound to get a variety of answers. There are french beans, large beans, small beans etc.,. and then some intelligent friend of your's might say that Java Beans are available as well. We'll leave all the other beans to the vegetable vendors and cooks to figure out and talk of Java Beans in this chapter. Before we try and figure out what a Java Bean is, let's explore the world of COMPONENTS and CONTAINERS. Let's try and get the basics clear with a true to life example. Suppose we had two programmers and a client. Programmer A has come out with the latest EMAIL program with a great user interface. The client hires A and is ready to buy his program, but fortunately or unfortunately the client is weak in English, and sends programmer A a letter saying " I will take your prouduct only if you can inculude spelcheck in it." Signed : client Seeing the pitiable state of his client's English, A takes it to be his moral responsibility to include spellcheck in his program. He neither has the time nor the patience to sit down and write a speller-checker program. So, he goes to the market, buys a speller-checker from B and includes it in his E-MAIL program. Now B's program is a component, which is added to A's program(container). Not every programmer who wrote the speller-checker could get the sign the deal with A(container). Only that program, which complied with, or followed all the set of rules put forth by A got it. We should drive home the fact that a COMPONENT must follow a certain set of rules given by the CONTAINER. Sun Microsystems developed a set of rules to enable java programs to be used as components, which they named 'Java Beans'. They also developed a reference container for these Java Beans to show the world the rules to be followed while using them. Create a subdirectory to work in. We have named our directory jb. Bare Minimum Requirements for learning Java Beans 1. Windows Operating System (95/98/NT) 2. JDK 1.1.x

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c:\jb\>edit zzz.java zzz.java import java.applet.* ; import java.awt .* ; public class zzz extends Applet { public void paint(Graphics g) { g.drawString("FrenchBean",10,10); } } This Program ends here.!!! We had this printed, just in case you were trying to turn pages, unable to believe that a Java Bean (an eight lettered word ), can be such a simple program. Then, what was all the hype about the technology we mentioned earlier ? There is one thing every person must understand about any new technology. It always makes life easier by doing all the complex jobs for us. So to succeed in the market it has to be very simple to use. Enough philosophy for now, let's get down to work . Java Bean is just another java program which can be used as a component in a container. An Ode to the Jars: Bungee jumping, skiing, scuba diving and surfing the net are the hobbies of millions, the world around, but did you ever try to think why surfing the net comes last on the list of hobbies ? It's because of the amount of time you have to wait before things come to you. When a person goes to a site on the Net and asks for some information, he is connected to the site where this information is available. The required data is in the form of a html document i.e. he first connects to the server, and gets the html document. Before being shown, the application (let's suppose it is some animation software), might ask for some .gif files, or some .class files etc. So, for retrieving each file, a special request has to be sent to the the server and the bytes have to be transferred to the client. Moreover, there is a lot of congestion on the net since the servers may be busy. Thus, the time taken for the transfer of the required bytes depends on the quality of the line, congestion on the server (too many clients accessing the same server) etc. Statistically speaking, even if we were to send you a message saying "Hello", 40 additional bytes of data (called as a TCP/IP header) would have to be transferred along with this message. So the gist is that each time there is a transfer of actual meaningful data from or http://www.vijaymukhi.com/documents/books/javajsp/chap7.html (2 of 7) [5/2/2008 10:59:47 PM]

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to the client, there is a lot of over head involved. Suppose your friend had given you a mystery novel. You start reading it and are interested. By the time you reached the climax and the mystery situation, you find out that the second half of the book is missing. Anxious to read the later chapters, you visit your friend, but in vain, as he's left for some other place and wouldn't be returning until later the next day. As there is no other alternative, you wait. Had you friend been thoughtful, he would have given you the other part too!

Sun Microsystems has been thoughtful enough and they introduced the concept of JARS. All the .class and other files relating to a particular application are compressed and put in the jar. So when the client asks for the html program containing the bean, the server is kind enough to send you the whole jar. Now you have all the information at one go. The client does not have to connect to the server again and again for the files relating to the particular program. In this way, both the server and the client save time. This has been done to make the life of net surfers easier. Mind you, the previous program can be called as a Java Bean only when put in a jar file. To compile zzz.java , give the following command c:\jb>javac zzz.java In order to create the manifest file, create a file with .mf extension. Here we give the filename as zzz.mf c:\jb>edit zzz.mf // The manifest file zzz.mf Manifest-Version: 1.0 Name: zzz.class Java-Bean: True The jar program creates a .jar file. It is a utility provided by Sun which puts all the required files of a particular application into the jar file. c:\jb>jar cfm zzz.jar zzz.mf zzz.class c:\jb>dir /w Volume in drive C has no label. Volume Serial Number is 1AD6-0B09

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Directory of C:\jb [.] [..] zzz.java zzz.class zzz.mf zzz.jar 4 File(s) 1,320 bytes 2 Dir(s) 545,153,024 bytes free The cfm options to jar file mean the following. -c create new archive -f specify archive file name -m include manifest information from specified manifest file The new archive to be created is given first, then the manifest file which contains the bean information and lastly the .class files which belong to the application. Note that only one class can be called a bean. The other class files that you specify are more like supportive files that contain code. c:\jb>copy zzz.jar c:\progra~1\bdk1.1\jars Sun Microsystem has a bean development kit which can be downloaded from their site. We have installed bdk1.1 . Here they have created a reference container for Java Beans, called the beanbox. The container looks at the jars subdirectory for all the jar files which have to be implemented in the Bean Development Kit (BDK). Hence we copy our .jar file into this subdirectory Now to see our bean work, we change to the bdk subdirectory and run a batch file viz. run.bat c:\jb>cd c:\progra~1\bdk1.1\beanbox c:\Program Files\BDK1.1\beanbox>run Voila! Our Java Bean - zzz is right there at the bottom of the Beanbox toolbar. Click and drag zzz into the beanbox container and you'll see a "Frenchbean" on the screen. Now, to bring the explicit button to the beanbox, we first click on the button and position the mouse on the container and then we click. Now that we have both a button and our Java Bean (zzz)in the beanbox container, let's learn how to connect both of them. First, we click on the freshly brought button and then look into the various options in the EDIT menuitem. Now, logically speaking, we want to see what the buttonpush can do for us, hence we checkout the action performed in the buttonpush option of the Events submenuitem. On clicking the action performed for a buttonpush, we find a jazzy red line with one end fixed at the button and the other end, free to move with the mouse. Now position the mouse on zzz and click on it. By doing this, we are actually connecting the button with our zzz Java Bean. http://www.vijaymukhi.com/documents/books/javajsp/chap7.html (4 of 7) [5/2/2008 10:59:47 PM]

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As soon as we click on the zzz Java Bean, an Event Target Dialog (a dialog box with this heading) pops up. This dialog box has a big list of functions which can be assigned to our pushbutton. Of the many functions in the dialog box only one seems to be both familiar and mysterious i.e. hide. So we select it and click on OK. Now let's emulate the disappearing act of Houdini. Press the pushbutton with a mouse click and see the "Frenchbean" disappear i.e. the Java Bean (zzz) in the beanbox container disappears. The Fundamentals of a Property : Now, it's time for some fun. To begin with, we first select the juggler icon from the toolbox (beanbox frame) and bring it into our Container. Can we interact with the juggler? This is the first question we should ask. The answer is, YES WE CAN !! There is a small window named the property sheet next to the beanbox container. This window has a property named animationrate which can be changed. By changing the value of the property, you will see the juggler juggling either slower or faster than before. What is a property? It is a variable that can be changed by the user. Now, It is very easy to create a variable and initialize it in the program itself. You can then have conditions and code that are executed when the variable is greater than some value or less than a certain value. When you change the value in the property sheet, a variable has to be created that accepts new values at run time and shows the effect immediately. To incorporate this feature, every variable has to have two functions that have to be preceded by either a get or a set. Such variables are called properties. Only two things can be done to a variable. You can either 'get' it or 'set' it. example : When i is initialised to 10 by giving i = 10 we are setting the variable i to 10 . and when i is used on the right side of the equalto i.e. something = i + 4, we are getting (returning) the value stored in variable i. The function which has 'set' has to be given a value whereas the function which has 'get' has to return some value. zzz.java http://www.vijaymukhi.com/documents/books/javajsp/chap7.html (5 of 7) [5/2/2008 10:59:47 PM]

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import java.applet.* ; import java.awt.* ; public class zzz extends Applet { int aa =10 ; public void paint (Graphics g) { g.drawString ("Great" + aa, 1, 1) ; } public void setxx(int i) { aa = i ; } public int getxx ( ) { return aa ; } } Create a batch file with the following commands and then execute it a.bat javac zzz.java jar cfm zzz.jar zzz.mf zzz.class cd c:\progra~1\bdk1.1\beanbox run Now when you bring in the bean into the container, you will see xx with the value 10 as a property in the PropertySheet. You can change this value and the resultant value will then be displayed in the Container. When xx =10, we see " Great 10 " in the beanbox and if we change it to xx = 100, we see " Great 100" in the beanbox .

Simulating our own function Previously, to make something disappear, we clicked on action performed for a push button and chose a target method ( assigned to the push button ) i.e . hide . We can now have our own function in the Event Target Dialog. For this we make modifications to the previous program. Remove the "getxx" and the "setxx" functions from the previous program, and put the

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following function in the code public void abc( ) { aa = 1000; repaint (); } Run the file a.bat. Bring the bean in the container and then the explicit button. Proceed to the Event Target Dialog by clicking on action performed of a buttonpush as before. The function abc() that we included in our code is up on the list. Select it and then click on OK. Now click on the button and see the value change on the screen. "Great 10 " now becomes " Great 1000" We've chosen names like abc so that we can easily find them as the first entry on the list.

Contents | Foreword | About the Authors | Introduction | Appendix |Chapter 1 |Chapter 2 |Chapter 3 |Chapter 4 |Chapter 5 |Chapter 6 | Chapter 7 |Chapter 8 |Chapter 9 |Chapter 10 |Chapter 11

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8. Java Beans and Java Server Pages Introduction The word Java Beans conjures up images of Coffee Beans or even Beanbags, but the Java Beans that we are talking about are related to Java. Java beans play a large role in JSP documents. A Java Bean is a Java component that works on any Java Virtual Machine. Packages If you had a class called Applet and if another user also called his class Applet, then whose Applet gets called, yours or his? To prevent a name clash, sun invented the concept of a package. They said that all classes created by Sun would start with java. Unfortunately this does nothing for a grouping. We would like all classes that deal with GUI issues to be grouped together. Thus we have one more level i.e. all GUI classes are part of java.awt and applet classes are a part of java.applet. Hence the full name of the class Applet is java.applet.Applet and java.applet is the package name which can be part of the import statement. Beans Before we get down to telling you what beans are, we would like you to do the following: We want you to change to c:\jswdk-1.0.1\examples\web-inf\jsp and there you will find a subdirectory called beans. Within this directory, create a subdirectory called yyy. Now create a file called zzz.java and enter the code given below. C:\jswdk-1.0.1\examples\web-inf\jsp\beans\yyy>edit zzz.java zzz.java package yyy; public class zzz { private String username = "mukhi"; public zzz() { System.out.println("Constructor"); } public void setusername(String name) { http://www.vijaymukhi.com/documents/books/javajsp/chap8.html (1 of 9) [5/2/2008 10:59:56 PM]

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username = name; System.out.println("setusername " + username); } public String getusername() { System.out.println("getusername" + username); return username; } } C:\jswdk-1.0.1\examples\web-inf\jsp\beans\yyy>javac zzz.java Since the first line is package yyy, in the beans directory you must create a subdirectory named yyy. The reason being, for the compiler to find packages, all the files that hold the classes contained in a package must reside in a directory bearing the package name. A Java Bean is a normal program. As we've seen in the previous chapter,it is a simple Java program; an applet can also be called a Java Bean. The only difference is that in a Bean some functions start with either a set or get, which is why we have setusername and getusername. Whenever a function begins with set or get, it relates to a property. That's what a Java Bean is made up of. The property here is username and not setusername or getusername. A variable or a property can either be used on the left or the right of the = sign. If it is on the left, then it gets a value, hence it takes one string as a parameter. Once you receive the value, what you do with it is up to you. In our program we store it in a public variable. Get is used with functions. When it is on the right hand side of the = sign, it returns a value and hence we are returning a string. C:\jswdk-1.0.1\examples\jsp>edit b1.jsp b1.jsp <jsp:useBean id="pp" scope="page" class="yyy.zzz" /> b1.jsp has an action called useBean followed by id=pp. pp is the id, we will use it to refer to our bean in the future. The actual name can be anything and there is nothing special about pp and class=yyy.zzz is because our bean zzz is in a package yyy. It is assumed that the bean will be in the sub-directory C:\jswdk-1.0.1\examples\web-inf\jsp\beans\ and the package yyy starts from this beans subdirectory onwards. Run the jsp file in the browser as before. http://www.vijaymukhi.com/documents/books/javajsp/chap8.html (2 of 9) [5/2/2008 10:59:56 PM]

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You get no errors. Check the dos screen of the Java Web Server where it will print 'Constructor' and then let's look at the generated code. ----------------// begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\b1.jsp";from=(0,0);to=(0,52)] // end // begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\b1.jsp";from=(0,0);to=(0,52)] yyy.zzz pp = null; boolean _jspx_specialpp = false; synchronized (pageContext) { pp= (yyy.zzz)pageContext.getAttribute("pp",PageContext.PAGE_SCOPE); if ( pp == null ) { _jspx_specialpp = true; try { pp = (yyy.zzz) Beans.instantiate(getClassLoader(), "yyy.zzz"); } catch (Exception exc) { throw new ServletException (" Cannot create bean of class "+"yyy.zzz"); } pageContext.setAttribute("pp", pp, PageContext.PAGE_SCOPE); } } if(_jspx_specialpp == true) { // end // begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\b1.jsp";from=(0,0);to=(0,52)] } // end out.print(_jspx_html_data[1]); ---------------------pp looks like yyy.zzz where yyy is the name of the package and zzz the name of the class. This is because in the JSP file the id was given as pp. pageContext has members like getAttribute, setAttribute and so on. pp is initialized using the getAttribute function. The second parameter is PageContext.PAGE_SCOPE, since that is what we had given in the JSP file. The next thing that you do is check if pp has a value. If it is Null, then Beans.instantiate will instantiate or create the bean. That means if the Bean is already loaded then you get a handle to it, if not then it is created. Instantiate is a static member in the Beans class. One of the parameters is the name of the Bean. We have given a very short explanation here; let's look at the next example to understand a lot more on Beans with JSP. zzz.java package yyy; public class zzz { private String username = "mukhi"; http://www.vijaymukhi.com/documents/books/javajsp/chap8.html (3 of 9) [5/2/2008 10:59:56 PM]

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public zzz() { System.out.println("Constructor"); } public void setusername(String name) { username = name; System.out.println("setusername " + username); } public String getusername() { System.out.println("getusername" + username); return username; } } b2.jsp <jsp:useBean id="pp" scope="page" class="yyy.zzz" /> hello , <jsp:getProperty name="pp" property="username" /> Output in browser hello , mukhi In the next example, we have a new action named getProperty with a name and a property. In our JSP file the property is username. This line will be replaced by the word mukhi. Look in the dos window and you'll see that the function getusername is called. This function returns the value of the variable username which is initialized to mukhi. Thus the tag <jsp:getProperty name="pp" property="username" /> is replaced by the string mukhi.

-------------// begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\b2.jsp";from=(3,8);to=(3,57)] out.print(JspRuntimeLibrary.toString(pp.getusername())); // end ---------------getproperty in the java generated code will become pp.getusername. setproperty is a function which is related to getproperty and is used in the next example. b3.jsp <%@ page import="yyy.zzz" %> <jsp:useBean id="pp" scope="page" class="yyy.zzz" /> http://www.vijaymukhi.com/documents/books/javajsp/chap8.html (4 of 9) [5/2/2008 10:59:56 PM]

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hello, <jsp:getProperty name="pp" property="username" /> <jsp:setProperty name="pp" property="username" value="no" />

hi, <jsp:getProperty name="pp" property="username" /> Output in browser hello, mukhi hi, no ---------// begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\b3.jsp";from=(5,0);to=(5,60)] pp.setusername("no"); // end out.print(_jspx_html_data[4]); // begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\b3.jsp";from=(6,8);to=(6,57)] out.print(JspRuntimeLibrary.toString(pp.getusername())); // end ----------With setusername, you give the name of the property and then the value. The value given here is 'no'. So you see mukhi and then no. The code is exactly the same. setusername is also called with the parameter having a value no and we initialize username with it. Scopes Let's talk about scopes in greater detail. There are four scopes, request, page, session and application. Each time you give the scope as session or request, the PageContext variable changes. b4.jsp <jsp:useBean id="pp" scope="session" class="yyy.zzz" /> ------------java file synchronized (session) { pp= (yyy.zzz) pageContext.getAttribute("pp",PageContext.SESSION_SCOPE); if ( pp == null ) { _jspx_specialpp = true; http://www.vijaymukhi.com/documents/books/javajsp/chap8.html (5 of 9) [5/2/2008 10:59:56 PM]

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try { pp = (yyy.zzz) Beans.instantiate(getClassLoader(), "yyy.zzz"); } catch (Exception exc) { throw new ServletException (" Cannot create bean of class "+"yyy.zzz"); } pageContext.setAttribute("pp", pp, PageContext.SESSION_SCOPE); } -----------------With scope as session, pageContext.getAttribute and setAttribute will have PageContext.SESSION_SCOPE. b5.jsp <jsp:useBean id="pp" scope="request" class="yyy.zzz" /> ------------java file synchronized (request) { pp= (yyy.zzz) pageContext.getAttribute("pp",PageContext.REQUEST_SCOPE); if ( pp == null ) { _jspx_specialpp = true; try { pp = (yyy.zzz) Beans.instantiate(getClassLoader(), "yyy.zzz"); } catch (Exception exc) { throw new ServletException (" Cannot create bean of class "+"yyy.zzz"); } pageContext.setAttribute("pp", pp, PageContext.REQUEST_SCOPE); } ----------With the scope as request, pageContext.getAttribute and setAttribute will have PageContext.REQUEST_SCOPE. Now we will consider two programs at a time b6.jsp and b7.jsp. b6.jsp <%@ page import="yyy.zzz" %> <jsp:useBean id="pp" scope="request" class="yyy.zzz" /> b6 , ello, <jsp:getProperty name="pp" property="username" /> <jsp:setProperty name="pp" property="username" value="no" />

llo, <jsp:getProperty name="pp" property="username" />

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click here b7.jsp <%@ page import="yyy.zzz" %> <jsp:useBean id="pp" scope="request" class="yyy.zzz" /> b7 , ello, <jsp:getProperty name="pp" property="username" /> <jsp:setProperty name="pp" property="username" value="no" />

llo, <jsp:getProperty name="pp" property="username" /> Here, we have two JSP files, b6 and b7. We are using the same Bean in both of them and the scope is request. The first file contains which will take us to the second page i.e. b7.jsp. When we click on the first page, yyy.zzz gets created, and the constructor is called. When we click on href, we move to b7. Since the scope in both is request, the constructor is called once more. The values are reinitialized and the variables are created from scratch. In this case, the page behaves like request. The bean is created each time, which means that it cannot remember its earlier values. Let's see an example where we give the scope as session. b8.jsp <%@ page import="yyy.zzz" %> <jsp:useBean id="pp" scope="session" class="yyy.zzz" /> b8 , <jsp:getProperty name="pp" property="username" /> <jsp:setProperty name="pp" property="username" value="no" />

llo, <jsp:getProperty name="pp" property="username" /> click here b9.jsp <%@ page import="yyy.zzz" %> http://www.vijaymukhi.com/documents/books/javajsp/chap8.html (7 of 9) [5/2/2008 10:59:56 PM]

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<jsp:useBean id="pp" scope="session" class="yyy.zzz" /> b9 , ello, <jsp:getProperty name="pp" property="username" /> <jsp:setProperty name="pp" property="username" value="no" />

llo, <jsp:getProperty name="pp" property="username" /> Here, the constructor is called only once and that happens when the Bean is loaded for the first time. When you click on the link, the constructor is not called. The Bean is not instantiated and the variables are not created again. They are persistent for that entire session. If you start a new browser, then a new session is created. When you give the scope as application, then the Bean and the variables retain their values till the server is shut down. Any client coming from any other site will see the values as they are on the server. It's like a page counter that keeps increasing on every visit to the page. Try it out with another copy of IE to understand it better. pageContext.getAttribute decides, depending upon the scope, whether the Bean should be instantiated or not. You decide on the scope depending upon the functionality of the JSP code. If the page scope is application, then everybody will be able to use it forever, but in case of session, it depends upon how you want to share the Bean. Conclusion In this chapter we have shown you how Java Server Pages receive from and send data to Java Beans. At the same time we also showed you how to create your own package. You are now also aware that setting the scope to the four different options will generate different results.

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Contents | Foreword | About the Authors | Introduction | Appendix |Chapter 1 |Chapter 2 |Chapter 3 |Chapter 4 |Chapter 5 |Chapter 6 | Chapter 7 |Chapter 8 |Chapter 9 |Chapter 10 |Chapter 11

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9. Cookies and a Shopping Cart Introduction Cookies have a number of uses for Web application developers and one of them is to track user sessions. Cookies originate on the server, where they are sent as instructions in the header of the HTTP response. In this chapter, we will see how Cookies are put to use in conjunction with JSP. You will also be shown how a shopping cart can be created. Remember that Java Server Pages are first turned into a servlet. In case there are any errors in your JSP script then they too are seen in the servlet. You may not see any error messages at this point but when you try to run the servlet and display the output in a browser, you will see the errors. You may get two types of errors. c1.jsp <%! int i=62745435354354353454354353454354353453454353434543543534543; %> <% out.println(i); %> Consider this example where the variable i has been initialized to a very large number. The question here is, will the JSP engine give an error while generating a servlet or will it show an error while displaying the output? --------------public class jsp_0005cc_00031_0002ejspc1_jsp_1 extends HttpJspBase { static char[][] _jspx_html_data = null; // begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\c1.jsp";from=(2,3);to=(2,71)] int i=62745435354354353454354353454354353453454353434543543534543; // end --------------The browser shows you just a simple error whereas the web server DOS window tells you in detail what the error is. Whenever you have a page directive 'buffer=kb', it should be a number because kb will be passed as a parameter, so when the servlet is compiled it gives an error.

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c2.jsp <%@ page buffer="kb" %> This shows the same error as seen earlier. A bit of showing off now. Here we have a class called JSPTest. c3.jsp <%! public class JSPTest { public String getName() { return "JSPTest"; } class Inner extends JSPTest { public String getName() { return "Inner"; } } } %> <% JSPTest jspTest = new JSPTest(); JSPTest.Inner inn = jspTest.new Inner(); out.println(" Base name: " + jspTest.getName()); out.println(" Inner name: " + inn.getName()); %> ----------------// begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\c3.jsp";from=(0,3);to=(10,0)] public class JSPTest { public String getName() { return "JSPTest"; } class Inner extends JSPTest { public String getName() { return "Inner"; } } } // end out.print(_jspx_html_data[1]); // begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\c3.jsp";from=(11,2);to=(15,0)] JSPTest jt = new JSPTest(); JSPTest.Inner inn = jt.new Inner(); out.println(" Base name: " + jt.getName()); out.println(" Inner name: " + inn.getName()); // end -------------http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (2 of 24) [5/2/2008 11:00:09 PM]

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Output: Base name: JSPTest Inner name: Inner C3.jsp has a public class named JSPTest. This class has a function named getName that returns a string. The string here is JSPTest. This class contains another class, which extends the same class. Class Inner is within JSPTest and it extends JSPTest. This is all legal. These types of classes are called inner classes. If Inner is an inner class then JSPTest should be an outer class! This is in one block of the script. In the next block, 'jt' is a variable that looks like JSPTest. 'inn' is another variable that looks like JSPTest.Inner. You can refer to this class because inner is a class in JSPTest. In C++, they are called Nested Classes. jspTest.new inner() is used to initialize inn. It is of significance to note that instead of 'new' we have used 'jt.new'. new is now part of jt. new ( ) is used to create the object and thus call the constructor. Therefore every time you have a class within a class, the outer class has its own new to create the inner classes. The function in the base class 'getName' returns JSPTest whereas the one in the inner class returns Inner. This has nothing to do with JSP. All Java code that you write in a Java program can be written in JSP too. In one of the previous chapters, we tried the bean example where we clicked on a link and went to another page. This can be done in another way by using jsp:forward. This will also take us to another page and the same rules apply. c4.jsp <jsp:plugin type="applet" code="zzz.class" width="160" height="150" codebase="/examples/jsp" jreversion="1.2" > <jsp:fallback> Hell

Bye The code of zzz.java is in c:\jswdk-1.0.1\examples\jsp zzz.java import java.awt.*; import java.applet.*;

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public class zzz extends Applet { int x,y; public void init() { x = 10 ; y = 20; } public void paint ( Graphics g) { g.drawString("Hi ", x , y); } public boolean mouseDown(Event e, int x1 , int y1) { x = x1 ; y = y1; return true; } } >javac zzz.java You can put any object you want along with jsp:plugin. A JSP page can have any plugin. Here we are giving type=applet, code=zzz.class along with the width and the height. In order to refresh your memory, the attribute width and height are given because the applet tag requires us to do so. This has already been explained in the first chapter. The jreversion is the version number of the Java runtime engine and the codebase attribute is the location from where the class file is to be picked up. In our case '/' is the JavaWebserver root directory and from there we are pointing to the examples/jsp subdirectory where the class file resides. Jsp:fallback will be looked at only when the object or the plugin statement gives an error. This is a lot like the 'try-catch' in Java. There are many types and applet is just one of them. A list of all the types can be found in the documentation. Just another way to add more content to the JSP page. -------------------// begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\c4.jsp";from=(1,0);to=(6,13)] /*Code generated for plugin*/ out.println (""); // end -----------------The html file received by the browser is as follows

Bye Click anywhere and you will find the word 'hell' following the click. All that the servlet does here is sends across the html file. Since this file has the applet tag, the browser asks for the applet. So the JSP engine sends the tags across with the attributes. The browser receives it and works as per the tags in the file. c5.jsp <jsp:forward page="e1.jsp" /> --------------------

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// begin [file="C:\\jswdk-1.0.1\\examples\\jsp\\c5.jsp";from=(1,0);to=(1,29)] if (true) { out.clear(); pageContext.forward("e1.jsp"); return; } // end -----------------You will directly come to another page, in this case you will come to e1.jsp. Let's see how we can call a servlet from JSP and then have the servlet load another JSP file. c.jsp <jsp:forward page="/servlet/yyy" /> c.jsp is located in c:\jswdk-1.0.1\examples\jsp subdirectory. It forwards to another page that the servlet yyy generates. yyy.java is located in c:\jswdk-1.0.1\webpages\web-inf\servlets. To load this servlet the url should be given as http://127.0.0.1:8080/examples/jsp/c.jsp. yyy.java import javax.servlet.*; import javax.servlet.http.*; public class yyy extends HttpServlet { public void doGet (HttpServletRequest request, HttpServletResponse response) { try { request.setAttribute ("servletName", "vijay"); ServletConfig a = getServletConfig(); ServletContext b = a.getServletContext(); RequestDispatcher c = b.getRequestDispatcher("/jsp/c6.jsp"); c.forward(request, response); } catch (Exception ex) { ex.printStackTrace (); } } } c6.jsp will be in the same directory as c.jsp i.e. c:\jswdk-1.0.1\examples\jsp. c6.jsp invoked by <% out.print (request.getAttribute("servletName").toString()); %>

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c.jsp will load the servlet yyy, where the function doGet is called. request.setAttribute will set the attribute named servletName to vijay. This is how we can create a variable within the servlet. Now anyone who has access to the servlet can access this variable vijay. This implies that any servlet can access the attribute 'servletName'. Instead of calling it 'servletName' you could have called it aaa. 'a' is a servletconfig which is initialized to the return value of getServletConfig. It is a function in HttpServlet. This has one member named ServletContext. The context in which the servlet is acting is the ServletContext and this function's return value is stored in b. When we call getRequestDispatcher from ServletContext, it will return a requestdispatcher and the parameter passed to this function is the page we wish to view. Here, we give /jsp/c6.jsp, which will load c6.jsp from the current directory-jsp and then finally, we say forward with our request and response. Now c6.jsp will be called. This JSP file will be compiled on the fly i.e. it will be converted into a servlet. In c6.jsp, we have request.getAttribute for servletName and hence it will give us vijay. This is how servlets communicate internally. In short, we have moved from one JSP page 'c.jsp', which became a servlet, to another servlet yyy which called a third servlet of c6.jsp and finally you see vijay displayed on the screen. Note that the first and the third servlet were originally JSP based Let's consider a simple bean. c7.jsp <jsp:useBean id="cb" scope="session" class="yyy.zzz" /> <jsp:setProperty name="cb" property="*" /> hi c7.jsp starts with jsp:usebean and the id is given as cb. The scope here is not important. The name of the class is yyy.zzz. Go to the web-inf directory and within the jsp\beans subdirectory create a new subdirectory yyy. Create a Java file called zzz.java here. It must contain the following code: c:\jswdk-1.0.1\examples\Web-inf\jsp\beans\yyy>edit zzz.java zzz.java package yyy; public class zzz { public void setxx(String a) http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (7 of 24) [5/2/2008 11:00:09 PM]

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{ System.out.println("setxx " + a); } public void setyy(String a) { System.out.println("setyy" + a); } public String getxx() { System.out.println("getxx"); return ""; } public String getyy() { System.out.println("getyy"); return ""; } } run it in the browser as http://127.0.0.1:8080/examples/jsp/c7.jsp?xx=hi&yy=bye The property for the bean cb is set by giving property='*'. This refers to the properties that are given in the form of name=value data in the url. Since the address given in the address bar has a '?' followed by xx=aaa&yy=bbb, the properties to be set will be that of xx and yy. So the JSP engine will call setxx and setyy with aaa and bbb in the Java Bean. If you had just given xx=aaa then only setxx would be called. If you are a good Bean designer, you will first find out the number of parameters you will be accepting and then accordingly create the properties in the Bean. So if you are accepting 7 parameters, you must create 7 properties with the same name in your Bean. Every property in the Bean will have get and set preceding the property name. '*' in the property will initialize all the properties in the Bean. You don't have to set all the properties yourself and this example proves that. The next program has been taken directly from the examples provided by Sun Microsystems. Here, we are considering an HTML file 'aa.html' within which there is code for creating a listbox. This file is to be placed in the examples/jsp subdirectory of jswdk-1.0.1. aa.html

Add Item:

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<SELECT NAME="item"> Beavis & Butt-head Video collection X-files movie Twin peaks tapes

We are create one listbox with three options. The first one is shown by default but you are allowed to choose any of them. When you click on the submit button the option selected will be given to the name 'item'. You will notice that here we have two submit buttons here, with the values add and remove respectively. Irrespective of the button clicked, the file that will be called is c8.jsp, which for the moment is on the same hard disk that we are operating from. The method given is post, items will be equal to the option selected and submit will be equal to either add or remove, these will go as parameters to the JSP file. Under normal circumstances submit isn't added as part of the parameter list, this happens only when there are two submits in the form. Once you click on submit, c8.jsp will be called. c8.jsp is stored in c:\jswdk-1.0.1\examples\jsp. c8.jsp <jsp:useBean id="cart" scope="session" class="ppp.qqq" /> <jsp:setProperty name="cart" property="*" /> <% cart.processRequest(request); %>
You have the following items in your cart:

<% String[] items = cart.getItems(); for (int i=0; i
1. <%= items[i] %> <% } %>

---

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qqq.java package ppp; import javax.servlet.http.*; import java.util.Vector; import java.util.Enumeration; public class qqq { Vector v = new Vector(); String submit = null; String item = null; private void addItem(String name) { v.addElement(name); } private void removeItem(String name) { v.removeElement(name); } public void setItem(String name) { item = name; } public void setSubmit(String s) { submit = s; } public String[] getItems() { String[] s = new String[v.size()]; v.copyInto(s); return s; } public void processRequest(HttpServletRequest request) { if (submit == null) addItem(item); if (submit.equals("add")) addItem(item); else if (submit.equals("remove")) removeItem(item); reset(); } private void reset() { submit = null; item = null; } } The bean that we are using is called ppp.qqq. At first the properties are set so setItem and http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (10 of 24) [5/2/2008 11:00:09 PM]

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setSubmit are called which initialize item and submit to the values from the html file after the user clicked on add. Then the cart.processRequest function in the bean is called with request as a parameter. (Remember request, like 'out', is a predefined object)

If you click on add, then submit will have the value add. Hence the addItem function will be called with item as a parameter. In addItem, we have only one line, which is v.addElement. v is a vector and it has a function named addElement. A vector is like an array, made up of similar objects. Using v.addElement we add the item name to the vector. String[] items = cart.getItems(); for (int i=0; i

<%= items[i] %> In order to display the selected items, getItems in the Bean is called. This function copies elements of the vector into a string array, which is then returned. Hence items in the JSP file will now contain these elements. As you already know, every string contains a length, which gives you the number of elements in the string. Thus items.length will now be the number of elements in the vector. The for loop is used to display each member. In order to display it as a bulleted list we have used li with <%=items[i]'. i is used along with the items to display every element. v.size represents the number of elements in the vector. For example, if you have 5 elements then v.size will give the value 5. v.copyInto will copy from the vector into a string array named s. Then s, an array of strings, is returned. This is how you can build a shopping cart. The concept of keeping the connection alive with a session in the servlet facilitates the creation of a virtual shopping mall. At this point start afresh. There will be now two separate sessions. In case you had used application instead of session, the process would have run forever for every new user. If the session was request or page then this exercise would not have been valid. The best way to test the Bean is by trying out these other scopes. Cookies The following example introduces the concept of Cookies. e25.jsp <%@ page session="true" %> <%

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Integer num = new Integer(100); session.putValue("num",num); String url = response.encodeURL("a1.jsp"); %> a1.jsp a1.jsp <%@ page session="true" %> <% Integer i = (Integer)session.getValue("num"); out.println("Num is " + i); %> In Internet Explorer, go to the menu option Tools and choose Internet Options. Then select the tabbed dialog option Security and click on the button labelled Custom Level. Finally, select prompt for the Cookie options. You must enable cookies in your browser. Also, select 'prompt'for the Cookies per-session option. You will now know when a cookie comes over since the browser will ask you for confirmation. A Cookie is stored as a file on disk. It contains a certain finite number of characters and is very small in size. The second important point to remember is that the cookie is transferred as a header. It is sent as the cookie name and it's value. The first line in the example is page session=true. It is not necessary to include this line because it is true by default. Then a variable named num is created which looks like integer. While calling the constructor, 100 is passed as a parameter. So num now holds the number 100. The next line in the script is session.putValue. This function putValue will create a variable named num and give it a value 100. Then we create a string variable called url that will be assigned the absolute address of a1.jsp. Finally a1.jsp will be evaluated to a1.jsp" as it is pure html. a1.jsp has a variable i of type integer. This variable is initialized to the return value of session.getValue(num). Remember, num was a variable created by session.putValue and it was initialized to 100. This object session remains active across the JSP pages and thus getValue of num returns 100. A user interacts with the web server in sessions. Thus, the session object allows you to create a variable in one file using putValue. You can then use this variable on another page. This method will work only if the page session is initialized to true. This is how you can transfer values from one file to another. Hence a1.jsp will print the value of i as 100. http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (12 of 24) [5/2/2008 11:00:09 PM]

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What are Cookies and how do Cookies work? Aha! You all know what Cookies are and how well they work for the stomach, but we are interested in a new type of Cookie, freshly baked from the Java shelf! So far you've only smelt the Cookie, now you get to taste it! The first time you connect to the web server, it will send you a cookie. As we have changed our cookie option to prompt, we will see a message box where we will click on 'more info'. Here we will be told that our cookie name is SESSIONID. It expires at the End of session and also the Data is To1011mC8999595236320718At. The web server sends a header with SetCookie: SESSIONID = To1011mC8999595236320718At. Now if you start another browser session the cookie name will be the same but the data will be To1012mC22314797589282154At i.e. it will be different. Each time a browser receives a cookie, it sends a header to the server the next time it connects. This header contains Cookie: SESSIONID = To1011mC8999595236320718At. This is how the web server can recognize one browser instance from another. To sum up, the web server starts by sending a cookie and the browser will send the same cookie back when it connects to the server again. The cookies are stored on your hard disk. Num is null If you disable cookies then you will get the output shown above as there is no way to distinguish one browser instance from another. A Cookie is a small amount of information which is sent by a servlet to the web browser. The browser saves this information on the hard disk and later on it can also be sent back to the server. A Cookie's value can uniquely identify a client. Hence Cookies are commonly used for session management. A Cookie has a name, a single value and it has attributes like comment, path, domain qualifiers, maximum age and version number. A large number of web browsers have bugs in how they handle the optional attributes, so please use them sparingly. They improve the interoperability of the servlet. Normally, a Cookie is sent to the browser one at a time and the browser is expected to support 20 Cookies for each web server, 300 Cookies in total and it may limit the Cookie size to 4k each. The browser is sent Cookies in the header and it returns Cookies to the servlet by adding fields to the http request header as mentioned earlier. Several Cookies might have the same name but different path attributes. Cookies affect the caching of the web pages that use them because HTTP 1.0 doesn't cache the pages with Cookies. There are two versions of the Cookies, version 0 is by Netscape and version 1, which is documented in rfc2109, is the original one. By default, Cookies are created in version 0 to ensure the best operability and the Cookies class implements cloneable. By default, all Cookies are returned to the server that sent them. A Cookie is sent to the browser by the servlet in the headers. That means that if the browser ever receives a Cookie from the server then each time it connects to the server, it will send the cookie in the header.

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C:\jswdk-1.0.1\webpages\web-inf\servlets> edit c1.java c1.java import java.io.*;import javax.servlet.*; import javax.servlet.http.*; public class c1 extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res)throws IOException, ServletException { Cookie c; c = new Cookie("zz7", "mukhi"); res.addCookie(c); PrintWriter out = res.getWriter(); out.println("Hi"); } } Let's consider this example. Here, c is an object that looks like Cookie. When we say c=new Cookie, we are passing two parameters to the constructor; one is a name 'zz7', which should be the name our cookie and the other is a value 'mukhi' i.e. the value of the cookie. Basically, we've created an object that looks like Cookie. res looks like HttpServletResponse and addCookie will add this cookie. The servlet uses HttpServletResponse whenever it wants to send some information to the server. All that the server does is, creates a header with the header variable Set-Cookie: and the value is given as zz7=mukhi. Set-Cookie: zz7=mukhi If you haven't enabled the Cookies option in your browser to Prompt, we suggest you do it now. This program is called when you load it in the browser. Give the url as http://127.0.0.1:8080/servlet/c1. On doing so, a message box will be displayed. Before clicking on 'Yes' select 'More Info'. It will tell you that the Cookie name is zz7 and below that it will show mukhi. This proves that your browser did receive a Cookie. Having understood the above program, let's look at the next program. c2.java import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class c2 extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (14 of 24) [5/2/2008 11:00:09 PM]

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ServletException { PrintWriter out = res.getWriter(); Cookie[] c = req.getCookies(); for (int i = 0; i < c.length; i++) out.println("cookie " + c[i].getName() + "=" + c[i].getValue()); out.println("Hi"); } } cookie zz7=mukhi Hi We sent one cookie and we received one cookie. Here, c is an array of Cookies. request.getCookies returns an array of Cookies. So, in the for loop we have i=0; i < c.length and then i++. Using getName and getValue, the name of the Cookie and the value given to it are printed. In our case c.length will be 1 because we have sent only one Cookie from the server. You can also send two Cookies at the same time. The next program demonstrates this. c3.java import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class c3 extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException { Cookie c; c = new Cookie("zz9", "mukhi"); c.setComment("Will this get dropped?"); c.setMaxAge(100); c.setPath(req.getServletPath()); c.setSecure(true); res.addCookie(c); c = new Cookie("zz10", "mukhi1"); c.setComment("Will this get dropped?1"); c.setMaxAge(10); c.setPath(req.getServletPath()); res.addCookie(c); PrintWriter out = res.getWriter(); out.println("H i" + req.getServletPath());

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} } In this program we have included Comment, which are some lines of text that you may want to add. setMaxAge decides how long the Cookie lives and setSecure is to use https - secure sockets layer to send this Cookie across. setPath means you are sending your computer path with your name and req.getServletPath will give the following : /examples/servlet/zzz. Now click on 'More Info' and you will observe that the other values, which were not filled in earlier, are now filled in. setMaxAge indicates the time period that the Cookie will be alive for. setPath specifies the path for the cookie to which the client should return the cookie. A cookie is visible to all pages in the directory you specify, and its subdirectorys. A Cookie's path must include the servlet that sent the Cookie. For example, /catalog makes the Cookie visible to all the Cookies on the server under /catalog. As we set the setMaxAge, the cookies 'expires' property now gives you an actual date and time. It is no longer a session cookie and netscape stores this information in a file named cookies.txt. The header now has an Expires=date added to it. In order to do so, use setPath and then use setVersion. If you specify the version as 0, the Cookie should comply with the original Netscape specification, if it is 1, then it should comply with rfc2109. Since Cookies are returned to a server, all servlets running within a server share Cookies. The next program shows how the domain, the path and the version can be retrieved. c4.java import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class c4 extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException { PrintWriter out = res.getWriter(); Cookie[] d = req.getCookies(); for (int i = 0; i < d.length; i++) { Cookie c = d[i]; out.println("cookie " + c.getName() + "=" + c.getValue()); out.print(c.getComment() + " " + c.getDomain() + " " + c.getMaxAge()); out.println(" " + c.getPath() + " " + c.getSecure() + " " + c.getVersion()); } out.println("Hi");

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} } In this example, the first Cookie comes over because you didn't set the path, the next two Cookies don't come over because you have set the path and the path is different. But how can one write a program that determines whether the Cookies have been disabled or enabled? Run the following program, c5.java. c5.java import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class c5 extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException { Cookie c;boolean h = false; String p = req.getParameter("ppp"); if (p == null) { c = new Cookie("vij4", "hi"); res.addCookie(c); res.sendRedirect( "/servlet/c5?ppp=no" ); } else if (p.equals("no")) { h = false; Cookie[] d = req.getCookies(); for (int i = 0; i < d.length; i++) { if (d[i].getName().equals ("vij4")) { if (d[i].getValue().equals("hi")) { h = true; break; } } } if ( h == true) res.sendRedirect( "/servlet/c6?aa=yes" ); else res.sendRedirect( "/servlet/c6?aa=no" ); } } } c6.java http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (17 of 24) [5/2/2008 11:00:09 PM]

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import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class c6 extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res)throws IOException, ServletException { PrintWriter out = res.getWriter(); String s = (String ) req.getParameter("aa"); out.println(s); } } c is a Cookie and h is a boolean with a value 'false'. p is a String that is initialized to the value given to ppp. ppp gets a value only when the user sends the url as http://127.0.0.1:8080/servlet/c5?ppp=xxx. Since we haven't given it in this manner, p will be null. The if condition becomes true and the control passes to the if statement. c is a Cookie where the variable vij4 is given the value 'hi'. This is added to the response and sendRedirect will redirect the browser to pick up another file from the disk. In the meantime the server will send the cookie to the browser and we can see that the value of the cookie vij4 is hi. The file is c5, the same servlet, but now with ppp having a value 'no'. Remember, the cookie is sent to the browser and redirect wrote the new url in the address bar of IE. The servlet gets called again but now the else statements are executed. Here, it is first checked whether the value of p is 'no'. This being true in our case, the statements within if are executed. The variable h is reinitialized to false and d is now declared as an array of Cookies. req.getCookies will return an array of Cookies. This is given to d. Within the for loop, it is checked whether a Cookie named vij exists. If there is one, then we break from the loop after initializing h to the value true. In our case with cookies off, the name 'vij4' does not exist, so h remains false. When the loop terminates, it is checked whether the value of h is true or false. If it is false, then the browser is redirected to another servlet c6 with the value 'no' given to aa. The servlet c6 now prints the value 'no' on the screen. If the value is 'yes', then the browser supports Cookies, because in that case it would already have a name 'vij4' stored. c7.java import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class c7 extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (18 of 24) [5/2/2008 11:00:09 PM]

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PrintWriter out = res.getWriter(); out.println("<TITLE>Current Shopping Cart Items"); out.println(""); String[] items = req.getParameterValues("item"); out.println("You currently have the following items in your cart:
"); if (items == null) { out.println("None"); } else { out.println("

"); for (int i = 0; i < items.length; i++) { out.println("
• " + items[i]); } out.println("

"); } out.println("

"); if (items != null) { for (int i = 0; i < items.length; i++) { out.println(""); } } out.println("Would you like to
"); out.println(""); out.println(""); out.println("

"); out.println(""); } } In c7.java, we are first printing the values of the array 'items' of type String. This variable is initialized to the value in the item parameter i.e. if the url contains ?item=hi , then the items array will contain one member named hi. If after the ? we had item=hi&item=bye, then the items array would have 2 members, hi and bye. A parameter in a url can have the same name repeated multiple times. Since we have given the url as http://127.0.0.1:8080/servlet/c7 there is no parameter value given to this servlet. Hence no items exist and we see 'None' displayed on the screen. The else block isn't executed and hence no list is displayed. Then a form is displayed on the screen. The for loop will not be executed as there are no items. Now within the text box, we want you to write aa and then click on the 'Add More Items' Button. req.getParameterValue(item) will now have the value as item=aa. With Java servlets and the HTTP protocol you can have items=hi&items=bye given along with the url. Note that you can have as many values given to the same parameter. getParameterValue will now give you an http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (19 of 24) [5/2/2008 11:00:09 PM]

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array of strings. You can then display all the strings. The servlet creates an html file along with a form. We have the input tag with type=hidden name =item and then the value of items. So if there are 6 items then we will have 6 input statements and all of them will be hidden. Hidden inputs will not be displayed on the screen. Now each time you say submit i.e. click on 'Add More Items' after writing in the text box, the program specified by action is called. Finally, we are calling the same servlet c7 and thus you see the same screen displayed again. This is one way of creating a shopping cart without using sessions. View Source <TITLE>Current Shopping Cart Items You currently have the following items in your cart:

• ggg
• ttt
• uuu

Would you like to

URL http://127.0.0.1:8080/servlet/c7?item=ggg&item=ttt&item=uuu A little more on Sessions...... This example will explain sessions once more. C:\jswdk-1.0.1\webpages\web-inf\servlets>edit xxx.java xxx.java import java.io.*; import java.net.*; import java.util.*; http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (20 of 24) [5/2/2008 11:00:09 PM]

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import javax.servlet.*; import javax.servlet.http.*; public class xxx extends HttpServlet { int i = 0; public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException { HttpSession s = request.getSession(); response.setContentType("text/html"); PrintWriter out = response.getWriter(); String h=" "; Integer o,o1; if (s.isNew()) { o = new Integer(0); h = "First Time"; s.putValue("acc", o); } else { h = "Once Again"; o = (Integer)s.getValue("acc"); o = new Integer(o.intValue() + 1); s.putValue("acc", o); } out.println(h + "

"); out.println("id " + s.getId() + "

"); out.println("Creation Time "+new Date(s.getCreationTime()) + "

"); out.println("Time of Last Access "+ new Date(s.getLastAccessedTime())+"

"); out.println("Max Inactive Interval "+ s.getMaxInactiveInterval()+"

"); out.println("getValue "+ s.getValue("acc")+"

"); out.println("Number of Previous Accesses "+o+"

"); String e[]; e = s.getValueNames(); for(int i=0; i <e.length; i++) out.println("Names "+e[i]+ "

"); } } Output First Time id To1015mC6692480998335292At Creation Time Tue Dec 26 17:45:51 GMT+05:30 2000 http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (21 of 24) [5/2/2008 11:00:09 PM]

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Time of Last Access Tue Dec 26 17:45:51 GMT+05:30 2000 Max Inactive Interval -1 getValue 0 Number of Previous Accesses 0 Names acc After clicking on the Refresh Button Once Again id To1015mC6692480998335292At Creation Time Tue Dec 26 17:45:51 GMT+05:30 2000 Time of Last Access Tue Dec 26 17:45:51 GMT+05:30 2000 Max Inactive Interval -1 getValue 1 Number of Previous Accesses 1 Names acc Once the servlet is loaded, the doGet function is called. A variable 's' that looks like HttpSession is created. It is initialized to the session object returned by request.getsession. response.setContentType will set the content type header to text/html. Now out is a variable that will generate our html file. The variable 'h' is of type String and is initialized to a blank space. Also, we have created two other variables o and o1 of type Integer. Every object that looks like session has a function named isNew. This function checks whether the session has been accessed in the past. At the moment, there has been no value given in this session, so isNew returns true. When the control enters the if statement, the variable o is given a value by calling the constructor with one parameter in Integer. Giving 0 as the value in the constructor will initialize o to 0. s.putvalue is one more function in HttpSession which takes the name of the variable and then the value to be given to this variable. The variable or the word here is 'acc'. Indirectly, acc is given the value 0. 'h', which is a string variable, is assigned the string 'First time'. At this point the else block will not be executed. The values of a few variables or properties in this session are then displayed. out.println with h will display 'First time'. Then we have s.getId. Every session is given a unique number. Thus, s.getId will display that unique id. The id is a number generated at random and is assigned only by the servlet container. It is implementation dependent. Then s.getCreationTime will return the time in milliseconds, i.e. the time when you last created the session. This is given to the Date constructor. This in turn will return a Date object which when displayed looks like the date format. The same rules apply for s.getLastAccessedTime. http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (22 of 24) [5/2/2008 11:00:09 PM]

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In our case the creation time and the date of last access will be similar. MaxInactiveInterval will tell you how much time has elapsed since you last accessed the session. When a client doesn't access a running session within a certain period of time, the session is invalidated. That means the servlet will discontinue the session. Here, if you say 10 minutes and do not access the session within 10 min, it will show a timeout. This is to make sure that the session doesn't go on indefinitely. The reason being, a user may decide to visit the Amazon site and not 'check out', he may simply disappear, or go to another site as he may have changed his mind. Here, if you give -1, a negative time, then the session doesn't timeout. s.getValue will give you the value of acc which is 0 at the moment. Thus it prints 0 along with the number of previous accesses, which again is the value of o i.e. 0. Remember, both are the same. Session has a function named getValueNames, which returns an array of Strings for the attributes or words present in the session. Since it is an array, we put it in a for loop. The variable i is initialized to 0. The loop will go on till the value of i reaches the length of the array. In our case, since we have only one attribute, the control will enter the loop only once, display acc and then quit. Now, when you click on the refresh button in IE, the session doesn't change but if you start a new copy of the browser then things will change. When doGet is called again i.e. when we press refresh, isNew returns false since acc is an attribute with a value in the session. So now the else block of the if statement is called. Here the current value of h is changed to 'Once again'. Then, the value of acc is retrieved using getValue. The Integer class has a function named intValue which converts the value to an int. o is reinitialized to a new value which is the old value plus 1. Finally, putValue sets acc to this new value. A session is an abstract entity created by the servlet. A servlet is loaded once and only once into memory whereas a session is created each time a new instance of a browser accesses the site. Thus a session is the same browser or the same user accessing different parts of the site. A new copy of IE would mean a new user and hence implies a new session. It is the cookie which distinguish one session from another. Using this technique, you can now create a Shopping Cart. Remember, the servlet is loaded only once in memory. Consider the following illustration- Each time you vist the Amazon site, if there is a servlet running on Amazon, you will be given a new session id. The session keeps track of what you buy. This is very similar to the value of acc, which keeps incrementing and yet remains unique http://www.vijaymukhi.com/documents/books/javajsp/chap9.html (23 of 24) [5/2/2008 11:00:09 PM]

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to the current session. All the attributes are session wise, hence you can now store all the books that you have purchased in the shopping cart. The session provides a way to identify a user across more than one page or a visit to a website. In effect, you can now store information about the user. Until a client joins a session isNew() returns true and on joining the session a value is inserted in that session. The session information is scoped only to the current copy of the browser. Therefore, the information stored in one session will not be directly visible to another. Conclusion In this chapter, you have seen how a shopping cart can be created.

Contents | Foreword | About the Authors | Introduction | Appendix |Chapter 1 |Chapter 2 |Chapter 3 |Chapter 4 |Chapter 5 |Chapter 6 | Chapter 7 |Chapter 8 |Chapter 9 |Chapter 10 |Chapter 11

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10. The Jakarta-Tomcat Project Create a simple JSP file in any subdirectory. We have created a new directory 'myprg' in c:\jakarta-tomcat3.2.1\webapps\examples\jsp and written our programs there. d1.jsp Vijay Mukhi Output in Browser Vijay Mukhi View Source Vijay Mukhi This program introduces the tag . This tag is similar to the jsp:tag which you are already familiar with. pp is not a predefined tag, it is our own custom tag. A custom tag allows you to extend a tag rather than use an existing tag. For those who need to have their memory refreshed, type in the following in the IE address bar. http://127.0.0.1:8080/examples/jsp/myprg/d1.jsp You will observe that the tag is ignored, since neither the browser nor the server understands . All that we see in IE or any browser is Vijay Mukhi and in View Source, we see the jsp file unchanged. The Java Web Server ignored the tag. The Java Web Server takes a long time to send back any output but the important thing to note is that the web server and the browser, both, ignored the tag as they don't understand it. There is no output in tha Java Server window and it is the servlet generated which send the jsp file over unchanged. Our next program includes minor changes. d2.jsp http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (1 of 31) [5/2/2008 11:00:33 PM]

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<%@ taglib uri="http://java.apache.org/tomcat/examples-taglib" prefix="pp" %> Vijay Mukhi Output in Browser org.apache.jasper.JasperException: No such tag log1 in the tag library imported with prefix pp It shows an error in the browser. The first statement within the body tag is a directive named taglib, followed by uri, an attribute, which stands for 'universal resource identifier'. The uri attribute is given a specific url. Another attribute required named prefix is initialized to pp, which is the name of our tag. When you try to load this JSP file, the browser shows you an error. The error says that it is an internal server error which means that we've upset the Java Web Server. The error clearly indicates that there is no tag log1 with the pp prefix. It does not recognize pp as a valid tag. In order to validate it, go to the following subdirectory- C:\jakarta-tomcat-3.2.1\webapps\examples\WEBINF. Here, you will find a file by the name of web.xml. The file web.xml and the WEB-INF subdirectory have now been standardized by the java servlet specification. In the earlier days, you could put whatever you wanted in whichever file and that could be located in any subdirectory. A major part of the Java servlet specification deals with the directories, their names and the files they should contain. web.xml talks about the web server. We have reproduced a part of the file that is relevant to our discussion. web.xml http://java.apache.org/tomcat/examples-taglib /WEB-INF/jsp/example-taglib.tld It starts with within which is ,this is the same url or name that we have given in the JSP file. The location it points to is /WEB-INF/jsp/example-taglib.tld. The uri is mapped to the location. The file example-taglib.tld contains the taglib description. Open this file by giving the path as follows: >edit C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\jsp\example-taglib.tld. http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (2 of 31) [5/2/2008 11:00:33 PM]

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example-taglib.tld 1.0 <jspversion>1.1 <shortname>simple A simple tab library for the examples ShowSource examples.ShowSource Display JSP sources jspFile <required>true true Since this file does not contain pp , we see an error. Now, we will add our own uri 'vijay' to the xml file and the tag pp in a tld file. d3.jsp <%@ taglib uri="vijay" prefix="pp" %> Vijay Mukhi web.xml .. http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (3 of 31) [5/2/2008 11:00:33 PM]

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.. < taglib-uri > vijay < taglib-location > /WEB-INF/jsp/ea.tld Add the following lines in web.xml somewhere at the bottom. Now you must restart the web server because web.xml is only read at startup time. Truncated Output in Browser org.apache.jasper.compiler.CompileException: C:\jakarta-tomcat3.2.1\webapps\examples\jsp\myprg\d3.jsp(2,0) Unable to open taglibrary vijay : C:\jakarta-tomcat3.2.1\webapps\examples\WEB-INF\jsp\ea.tld (The system cannot find the file specified) The web server starts fine but when we load d3.jsp in the browser we get the error as shown above. When the Java Web Server starts, it reads web.xml. There it meets a tag named taglib. Within that it finds a tag tagliburi which encloses a name, vijay. Then it looks at another tag taglib-location, which holds the name of the file /WEB-INF/jsp/ea.tld. It looks for ea.tld as the details of vijay are stored in it. When the server encounters a jsp tag starting with pp, it looks at one of the earlier lines to check for a uri associated with this tag. This is done by using the taglib directive where we have given the uri as vijay and the prefix as pp. Vijay in web.xml points to a file named ea.tld. The file ea.tld is not present in the directory because we didn't create it. Hence the error. Create this file in the location specified in the web.xml file but leave it empty. C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\jsp>copy con ea.tld .............................................leave a blankline press {Enter} ^Z 1 file(s) copied Shutdown and restart the Java Web Server. Once again, we get errors again. Let's go back and load d3.jsp Output in Browser org.apache.jasper.compiler.CompileException: C:\jakarta-tomcat3.2.1\webapps\examples\jsp\myprg\d3.jsp(2,0) Unable to open taglibrary vijay : Parse Error in the tag library http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (4 of 31) [5/2/2008 11:00:33 PM]

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descriptor: Document root element is missing. You get the error since the file ea.tld is empty, although the error does say this. The tld extension is a short form for tag library description. It is an xml file and every xml file must begin with xml version=1.0. As of now the only version that xml understands is version 1.0 . Key in the following few lines in the tld file to have this error disappear. What we are now learning are the rules of xml. ea.tld The second line that contains DOCTYPE taglib.... The word following DOCTYPE - taglib, is the starting tag or the first tag or the document root. It indicates the beginning and an end of the xml document. In other words it is the first tag we will encounter. PUBLIC is some sort of an identifier and the rules of this document are stored in web-jsptaglibrary_1_1.dtd. These rules decide on the other tags to be allowed in the document, their order and how many times they can appear. It is like a syntax check which HTML desn't have. This also means that we can't write just anything in a tld file, it has to follow the rules which are specified in the dtd. XML is called the eXtensible Markup Language because it is used to write other markup languages. These rule are specified through the dtd which is also an xml file Truncated Output in Browser org.apache.jasper.compiler.CompileException: C:\jakarta-tomcat3.2.1\webapps\examples\jsp\myprg\d3.jsp(2,0) Unable to open taglibrary vijay : Parse Error in the tag library descriptor: Element taglib requires additional elements The error is now different from the earlier one where there was no mention of a tag taglib in the file. The document type is taglib, but it needs more elements and one of them is a tag named pp. ea.tld 1.0 <shortname>pp log1 examples.xxx Truncated Output in Browser http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (5 of 31) [5/2/2008 11:00:33 PM]

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javax.servlet.ServletException: examples/xxx Root Cause java.lang.NoClassDefFoundError: examples/xxx The error tells us that we need a class named examples.xxx. The taglibrary is pp and has the version 1.0 which can be any number that we like. This library has a tag named log1. The tagclass associated with this name will be loaded or called when some action has to be taken on the tag. Since we do not have this class, we get the error. tagclass refers to the Java file that contains the code. Since everything is bundled in a package, xxx.java is included in the package 'examples; and hence the first line is package examples; The directory where xxx.class would be searched for by default is C:\jakarta-tomcat3.2.1\webapps\examples\WEB-INF\classes and because of the package statement, we have to move down into the examples sub-directory. C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes >cd examples C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes\examples>edit xxx.java xxx.java package examples; public class xxx { public xxx() { System.out.println("In Constructor xxx"); } } The first line is package examples. This directory will be searched for from the classpath. The servlet specification says that all your class files should be in web-inf\classes and all jar files in web-inf\jar. Hence examples is created in web-inf\classes. Compile the java file and reload the jsp file in yur browswe. The java file will give you an error. Truncated Output in Browser javax.servlet.ServletException: (class: jsp/myprg/_0002fjsp_0002fmyprg_0002fd_00033_0002ejspd3_jsp_0, method: _jspService signature: (Ljavax/servlet/http/HttpServletRequest;Ljavax/servlet/http/HttpServletResponse;)V) Incompatible object argument for function call In english, this error means that we have to derive xxx from some class as there are some functions which are being called by the Java Web Server and they do not seem to exist in our servlet.

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C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes\examples>javac xxx.java xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase { public xxx() { System.out.println("In Constructor xxx"); } } We get 2 errors. The first one is at the import statement. Whenever we get an error at an import it means that we have not specified a jar file in our classpath. C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes\examples>set CLASSPATH=c:\jakartatomcat.3.2.1\lib\servlet.jar;%CLASSPATH% C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes\examples>javac xxx.java Now the earlier import error disappears and we get another one stating that ExampleTagBase cannot be found. Once again we have to set classpath to the sub directory before examples, i.e. upto classes. Set classpath=C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes;%CLASSPATH% Now javac does not give us any errors. If our Java file or class file has to represent a tag, then it should extend a class that contains all the code to represent a tag. Hence we have extended xxx from ExampleTagBase. This class is in the same subdirectory but it in turn refers to other classes. In case you don't see the same results as we do, then shutdown the server and restart it. Load d3.jsp in your browser and the Java Web Server dos box will show 'In Constructor xxx'. This means that the JSP engine on seeing pp:log1, instantiated xxx. Hence the constructor is called. In addition, the View Source now shows us the following. This proves that the Java Web Server has now changed the file and then sent it across. View Source http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (7 of 31) [5/2/2008 11:00:33 PM]

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A look at the next program xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return SKIP_BODY; } } This program implements a function named doStartTag. The return value is SKIP_BODY. This is a number which we will concern ourselves with it a little later. In the web server console we will now see two lines of output which tell us that the function doStartTag is called. Let's add one more function named doEndTag. xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return SKIP_BODY; } public int doEndTag() { System.out.println("doEndTag"); return EVAL_PAGE; } }

The output in the dos box clearly tells us that at first the JSP engine calls doStartTag and then doEndTag. This implies that the tags used in the JSP file are calling Java code in xxx. doStartTag returns SKIP_BODY http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (8 of 31) [5/2/2008 11:00:33 PM]

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whereas doEndTag returns EVAL_PAGE. These return values are numbers or ints. We still do not see any output in the IE window. xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } public int doEndTag() { System.out.println("doEndTag"); return EVAL_PAGE; } } C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes\examples>javac xxx.java xxx.java:11: Undefined variable: EVAL_BODY_TAG return EVAL_BODY_TAG; ^ 1 error On compiling, we get an error. This is because we have used EVAL_BODY_TAG, a variable that the compiler does not understand. We thought it would exist in ExampleTagBase but it is a member of BodyTag. To get rid of this error we have to implement an interface named BodyTag. This is demonstrated in the next example. xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (9 of 31) [5/2/2008 11:00:33 PM]

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public int doEndTag() { System.out.println("doEndTag"); return EVAL_PAGE; } } When you implement from an interface, the interface either contains variables that have been given values or it can contain function prototypes. Since the interface BodyTag also contains variables, the error disappears. In IE, we see no errors provided we shutdown the server, move one directory up, deltree work, md work, go back to bin and then run startup again. In the next program, we have added a function named doAfterBody. xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } public int doAfterBody() { System.out.println("doAfterBody1 " ); return SKIP_BODY; } } At first doStartTag is called and because this function returns EVAL_BODY_TAG, the JSP engine will now call doAfterBody. But if you replace EVAL_BODY_TAG with SKIP_BODY, the function doAfterBody will not be called. Thus the JSP engine/Java web server will first call doStartTag and depending on what it returns it will or will not call doAfterBody. Tags in html can either have some content or they can be empty. In our case we have vijay mukhi, which is our body. This can be retrieved in doAfterBody. Let's understand how this is done.

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xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } public int doAfterBody() { System.out.println("doAfterBody1 " ); String s = bodyOut.getString(); System.out.println(s); return SKIP_BODY; } } In order to do this, use bodyOut.getString in doAfterBody. bodyOut is an object in ExampleTagBase and getString is a function in bodyOut which returns the string of the body, which in our case is Vijay Mukhi. A quick look at d3.jsp in case you have forgotten d3.jsp <%@ taglib uri="vijay" prefix="pp" %> Vijay Mukhi BodyOut is an object which is an instance of BodyContent. This string will only be dispalyed in the web server console window. To see it in the browser, we have to use some more functions like writeOut and getEnclosingWriter() in bodyOut. These functions throw an exception. Merely saying 'doAfterBody throws IOException' will not work because the signature changes. So, we must put the code of doAfterBody in a try and catch. xxx.java package examples;

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import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } public int doAfterBody() { try { System.out.println("doAfterBody1 " ); String s = bodyOut.getString(); System.out.println(s); bodyOut.writeOut(bodyOut.getEnclosingWriter()); } catch (Exception e) {} return SKIP_BODY; } } Output in Browser Vijay Mukhi The function bodyOut.getEnclosingWriter returns an object that looks like java.io.Writer and bodyOut.writeOut requires a java.io.Writer. writeOut will write the entire body as an html page. In doAfterBody, you can actually write into your html page which will then be sent over. Thus, writeOut will actually send the contents between our tag log1 in our jsp file, which was Vijay Mukhi, over to the web server. xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (12 of 31) [5/2/2008 11:00:33 PM]

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public int doAfterBody() { System.out.println("doAfterBody1 " ); return SKIP_BODY; } public void doInitBody() { System.out.println("doInitBody " ); } } As you can see in your dos box, doStartTag is called first, then doInitBody is called and finally doAfterBody. This happens because we return EVAL_BODY_TAG in doStartTag. Since doAfterBody returns SKIP_BODY, the process terminates. If it were to return EVAL_BODY_TAG then you would keep seeing Vijay Mukhi indefinitely. xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } public int doAfterBody () { try { System.out.println("doAfterBody1 " ); String s = bodyOut.getString(); System.out.println(s); bodyOut.writeOut(bodyOut.getEnclosingWriter()); } catch (Exception e) {} return EVAL_BODY_TAG; } public void doInitBody() { System.out.println("doInitBody " ); } http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (13 of 31) [5/2/2008 11:00:33 PM]

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} This means doAfterBody is invoked after each body evaluation. On returning EVAL_BODY_TAG, a new evaluation of the body will start and it will follow the same procedure i.e. calling doAfterBody. The entire roller coaster stops it sees get SKIP_BODY. The JSP engine calls these function for us to execute certain tasks in them. doInitBody is called only once and if we have any one time tasks to perform, we place them in doInitBody. In doAfterBody we receive the content the tag encloses and can create an html file which will be sent across to the browser. We have now learnt that when there is a tag in a JSP file, certain code in the class file gets called. Note that these tags can also have attributes. The next example deals with an attribute in the tag. C:\jakarta-tomcat-3.2.1\webapps\examples\jsp\myprg>edit d4.jsp d4.jsp <%@ taglib uri="vijay" prefix="pp" %> Vijay Mukhi xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } public int doAfterBody() { try { System.out.println("doAfterBody1 " ); String s = bodyOut.getString(); System.out.println(s); bodyOut.writeOut(bodyOut.getEnclosingWriter()); }

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catch (Exception e) {} return SKIP_BODY; } public void doInitBody() { System.out.println("doInitBody " ); } public void setAa(String v) { System.out.println("setaa " + v); } } Here, we have an attribute named aa which is initialized to hell. If we stop here, we will not get an error even though in ea.tld we have not specified the attributes that are allowed with our tag log1, and a prefix of pp. In the browser run d4.jsp and not d3.jsp. If we remove the function named setaa from xxx then we will get the following error in our browser. Truncated Output in Browser javax.servlet.ServletException: examples.xxx: method setAa(Ljava/lang/String;)V not found So in ea.tld, we have to say attribute /attribute within the tag and within it we specify the name of our attribute i.e. aa. C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\jsp>edit ea.tld ea.tld 1.0 <shortname>pp log1 examples.xxx aa aa now becomes an attribute. For it to be an attribute, you need a function named setaa in xxx.java. This function takes one string as a parameter, named v in this case. The value of v is hell. C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes\examples>edit xxx.java http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (15 of 31) [5/2/2008 11:00:33 PM]

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xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } public int doAfterBody() { try { System.out.println("doAfterBody1 " ); String s = bodyOut.getString(); System.out.println(s); bodyOut.writeOut(bodyOut.getEnclosingWriter()); } catch (Exception e) {} return SKIP_BODY; } public void doInitBody() { System.out.println("doInitBody " ); } public void setaa(String v) { System.out.println("setaa " + v); } } When you see the dos screen, you will realize that the attributes are called after the constructor. The value of v is hell, the same value that the attribute had. There is no getaa in the class file. In a way, this class file resembles a Java Bean that has a set and a get for the attributes. A tag can have a subtag named required. When you say that the tag required encloses a value true, then you have to have to have that attribute as part of the tag. It is mandatory and not having it present will get us an error. ea.tld http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (16 of 31) [5/2/2008 11:00:33 PM]

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1.0 <shortname>pp log1 examples.xxx aa <required>true d5.jsp <%@ taglib uri="vijay" prefix="pp" %> Vijay Mukhi We do not have an attribute named aa which is mandatory in the ea.tld file. The error is as follows

Truncated Output in Browser org.apache.jasper.compiler.CompileException: C:\jakarta-tomcat3.2.1\webapps\examples\jsp\myprg\d4.jsp(3,0) According to the TLD attribute aa is mandatory for tag log1 Now that we have learnt how we can have tags and how a class file is loaded to work with tags, let's go back to the basics again. The class Tag is a base class. All the other tags are derived from Tag. The class BodyTag adds two more methods. If you want support tags then you will have to implement Tag. Let's start with the smallest one. Here we say public class xxx implements tag. xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx implements Tag {

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} >javac zzz.java xxx.java:3: class examples.xxx must be declared abstract. It does not define void release() from interface javax.servlet.jsp.tagext.Tag. public class xxx implements Tag ^ xxx.java:3: class examples.xxx must be declared abstract. It does not define int doEndTag() from interface javax.servlet.jsp.tagext.Tag. public class xxx implements Tag ^ xxx.java:3: class examples.xxx must be declared abstract. It does not define void setPageContext(javax.servlet.jsp.PageContext) from interface javax.servlet.jsp .tagext.Tag. public class xxx implements Tag ^ xxx.java:3: class examples.xxx must be declared abstract. It does not define javax.servlet.jsp.tagext.Tag getParent() from interface javax.servlet.jsp.tagext.Tag. public class xxx implements Tag ^ xxx.java:3: class examples.xxx must be declared abstract. It does not define void setParent(javax.servlet.jsp.tagext.Tag) from interface javax.servlet.jsp.tagext.Tag. public class xxx implements Tag ^ 6 errors On compiling, you will get 6 errors. You can get rid of the errors by including the word abstract. xxx.java package examples; import javax.servlet.jsp.tagext.*; public abstract class xxx implements Tag { } But if someone derives from xxx, he will get errors. Basically, there are 6 functions in tag that have to be implemented. So, we remove abstract and place these 6 functions one by one. The 6 functions are: release, doEndTag, setParent ,getParent, setPageContext and doStartTag. d6.jsp http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (18 of 31) [5/2/2008 11:00:33 PM]

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<%@ taglib uri="vijay" prefix="pp" %> Vijay Mukhi

ea.tld 1.0 <shortname>pp log1 examples.xxx xxx.java package examples; import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; public class xxx implements Tag { protected Tag parent; public void release() { System.out.println("release"); } public int doEndTag() { System.out.println("doEndTag"); return EVAL_PAGE; } public void setParent(Tag parent) { System.out.println("setParent"); this.parent = parent; } public Tag getParent() { System.out.println("getParent"); return this.parent; } public void setPageContext(PageContext pageContext) { System.out.println("setPageContext"); http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (19 of 31) [5/2/2008 11:00:33 PM]

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} public int doStartTag() { System.out.println("doStartTag"); return SKIP_BODY; } } When you open d6.jsp in the browser you will get the following error Truncated Output in Browser javax.servlet.ServletException: examples/xxx The reason we get the error is because the jsp engine expects the class to implement from both Tag and BodyTag. C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes\examples>edit xxx.java xxx.java package examples; import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; public class xxx implements Tag,BodyTag { protected Tag parent; public void release() { System.out.println("release"); } public int doEndTag() { System.out.println("doEndTag"); return EVAL_PAGE; } public void setParent(Tag parent) { System.out.println("setParent"); this.parent = parent; } public Tag getParent() { System.out.println("getParent"); return this.parent; } public void setPageContext(PageContext pageContext) { System.out.println("setPageContext"); } public int doStartTag() {

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System.out.println("doStartTag"); return SKIP_BODY; } } C:\jakarta-tomcat-3.2.1\webapps\examples\WEB-INF\classes\examples>javac xxx.java xxx.java:5: class examples.xxx must be declared abstract. It does not define void setBodyContent(javax.servlet.jsp.tagext.BodyContent) from interface javax.servlet.jsp.tagext.BodyTag. public class xxx implements Tag,BodyTag ^ xxx.java:5: class examples.xxx must be declared abstract. It does not define void doInitBody() from interface javax.servlet.jsp.tagext.BodyTag. public class xxx implements Tag,BodyTag ^ xxx.java:5: class examples.xxx must be declared abstract. It does not define int doAfterBody() from interface javax.servlet.jsp.tagext.BodyTag. public class xxx implements Tag,BodyTag ^ 3 errors Once again the error appears because of the interface. xxx.java package examples; import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; public class xxx implements Tag,BodyTag { protected Tag parent; protected BodyContent bodyOut; protected PageContext pageContext; public void release() { System.out.println("release"); } public int doEndTag() { System.out.println("doEndTag"); return EVAL_PAGE; } public void setParent(Tag parent) { System.out.println("setParent");

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this.parent = parent; } public Tag getParent() { System.out.println("getParent"); return this.parent; } public void setPageContext(PageContext pageContext) { this.pageContext = pageContext; System.out.println("setPageContext"); } public int doStartTag() { System.out.println("doStartTag"); return EVAL_BODY_TAG; } public void doInitBody() throws JspException { System.out.println("doInitBody"); } public int doAfterBody() throws JspException { System.out.println("doAfterBody"); return SKIP_BODY; } public void setBodyContent(BodyContent bodyOut) { System.out.println("setBodyContent"); this.bodyOut = bodyOut; } } Output in Server window setPageContext setParent doStartTag setBodyContent doInitBody doAfterBody doEndTag release 8 functions are called in all. The first function that is called is setPageContext. This function receives a parameter named pageContext. It takes this object that looks like PageContext and stores it in a public variable of the same name i.e. pageContext. If we use this.pageContext we are referring to the public variable. Without this, pageContext refers to the parameter passed to the function. This is how we initialize the first of the three public variables in our class. Recall how we used bodyOut earlier. The next function to be called is setParent, which as the name suggests, refers to the parent Tag which it is passes as a parameter and initializes the public variable parent. http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (22 of 31) [5/2/2008 11:00:33 PM]

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Thereafter, doStartTag and doEndTag are called and then finally, release is called. getParent doesn't ever get called. This is the only function that isn't called and the order in which they are called remains constant. In addition, three more functions which refer to the body are also called. They are doInitBody, doAfterBody and setBodyContent. The function setBodyContent is the one that initializes bodyOut, which we use to reference our tag. First doStartTag is called and if we returns EVAL_BODY_TAG in this function, then SetBodyContent, doInitBody and doAfterTag are called. The exampleTagClass, which we derived from in the earlier examples has two to three variables - Parent, bodyOut, pageContext. These were initialized in the functions and were mandatory in the required classes. That means if you want to create your own class then you can name it anything you like. So you don't have to use ExampleTagClass. All that you have to do is derive from Tag and BodyTag and make sure that the functions do what we have done. ExampleTagClass is useful because we do not want to implement so many functions and we can call it a helper class. In doStartTag, if you return SKIP_BODY, then setBodyContent isn't called. so you don't require an object that looks like BodyContent. BodyContent is a subclass of jspwriter. If doStartTag returns SKIP_BODY then none of the tags from BodyTag will ever be called. It is only if doStartTag returns EVAL_BODY_TAG that the rest of them are called. Let's consider another set of examples. We will keep reminding you that attributes and methods are called before any other function. Here, we have the same old tag pp:log1. A JSP tag starts with <% and here we use the same = with a name memb. d6.jsp <%@ taglib uri="vijay" prefix="pp" %> Vijay <%= memb %> On doing so, you will get the following error. Output in Browser http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (23 of 31) [5/2/2008 11:00:33 PM]

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org.apache.jasper.JasperException: Unable to compile class for JSPC:\jakarta-tomcat3.2.1\work\localhost_8080%2Fexamples\_0002fjsp_0002fmyprg_0002fd_00036_0002ejspd6_jsp_1.java:79: Undefined variable: memb out.print( memb ); This is an error because the jsp engine cannot find a variable named memb. In our next program, we have the same doStartTag, doAfterBody, doInitBody and are doing exactly the same thing as earlier. But we have made an addition; we have added one more line where we are calling a function pageContext.setAttribute(). So in other words, we are creating a variable named memb and initializing it to Sonal. xxx.java package examples; import javax.servlet.jsp.tagext.*; public class xxx extends ExampleTagBase implements BodyTag { public xxx() { System.out.println("In Constructor xxx"); } public int doStartTag() { System.out.println("doStartTag1 " ); return EVAL_BODY_TAG; } public int doAfterBody() { try { System.out.println("doAfterBody1 " ); String s = bodyOut.getString(); System.out.println(s); bodyOut.writeOut(bodyOut.getEnclosingWriter()); } catch (Exception e) {} return SKIP_BODY; } public void doInitBody() { System.out.println("doInitBody " ); pageContext.setAttribute("memb", "Sonal"); } }

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You see the same error as before. This means that we now have to go back to our ea.tld file, and introduce a new tag named a teiclass. ea.tld 1.0 <shortname>pp log1 examples.xxx examples.yyy yyy.java package examples; import javax.servlet.jsp.tagext.*; public class yyy extends TagExtraInfo { public VariableInfo[] getVariableInfo(TagData data) { return new VariableInfo[] { new VariableInfo("memb","String",true,VariableInfo.NESTED) }; } } >javac yyy.java In the yyy class, which is derived from the TagExtraInfo tag, we once again start with the package examples. Class yyy extends TagExtraInfo. getVariableInfo is a member of this class, which returns an array of VariableInfo. Here, we're returning an object that looks like an array of VariableInfo. Instead of giving a semicolon to end the statement, we are giving an open curly bracket. At this point, we are creating the array VariableInfo and initializing it at the same time. The syntax is important. Since it is an array, you can say new as many times as you want, one below the other for each member of the array. Here, we are creating memb, a variable of type string, and VariableInfo.NESTED indicates that it is nested one within the other. It will display Vijay Sonal in the browser and in the Java Web Server, and of course no errors! What if, in doStartTag, we give pageContext.setAttribute("memb", Sonal2") and in doAfterBody we give pageContext.setAttribute("memb", Sonal3"), as shown below. http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (25 of 31) [5/2/2008 11:00:33 PM]

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public int doStartTag() { System.out.println("doStartTag2 " ); pageContext.setAttribute("memb", "Sonal2"); return EVAL_BODY_TAG; } public int doAfterBody() { try { System.out.println("doAfterBody1 " ); pageContext.setAttribute("memb", "Sonal3"); String s = bodyOut.getString(); System.out.println(s); bodyOut.writeOut(bodyOut.getEnclosingWriter()); } catch (Exception e) {} return SKIP_BODY; } We have initialized memb in three differnet places. Yet we see Sonal. The doStartTag function is called right at the beginning. Here, memb should have been initialized to Sonal2, but it is in doAfterBody that we say bodyout.write. doAfterBody has a setattribute too. In such a case, doAfterBody has no effect. Therefore, as the setattribute in doafterbody is ignored, Sonal will be displayed. Hence you should not use setAttribute everywhere as it will be ignored. NESTED is the scope for the variable. If you say nested then the variable is available between the start and the end tag. If you change nested to AT_BEGIN, then it is available from that tag to the end of the page. But if you use AT_END, then it is available from the end of the tag to the end of the page. In the following example, we have used memb twice. d8.jsp <%@ taglib uri="vijay" prefix="pp" %> Vijay <%= memb %>

Vijay1 <%=memb %> xxx.java remains the same as before yyy.java http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (26 of 31) [5/2/2008 11:00:33 PM]

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package examples; import javax.servlet.jsp.tagext.*; public class yyy extends TagExtraInfo { public VariableInfo[] getVariableInfo(TagData data) { return new VariableInfo[] { new VariableInfo("memb","String",true,VariableInfo.NESTED) }; } } Truncated Output in Browser org.apache.jasper.JasperException: Unable to compile class for JSPc:\jakarta-tomcat3.2.1\work\localhost_8080%2Fexamples\_0002fjsp_0002fmyprg_0002fd_00036_0002ejspd6_jsp_1.java:109: Undefined variable: memb out.print( memb ); If you use NESTED, then you will get an error as shown above. yyy.java package examples; import javax.servlet.jsp.tagext.*; public class yyy extends TagExtraInfo { public VariableInfo[] getVariableInfo(TagData data) { return new VariableInfo[] { new VariableInfo("memb","String",true,VariableInfo.AT_BEGIN) }; } } Output in Browser Vijay Mukhi Sonal Vijay1 Sonal3 In the Server Window Vijay Mukhi Sonal AT_BEGIN means that they are now 2 different values to the same variable memb. yyy.java package examples; import javax.servlet.jsp.tagext.*; http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (27 of 31) [5/2/2008 11:00:33 PM]

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public class yyy extends TagExtraInfo { public VariableInfo[] getVariableInfo(TagData data) { return new VariableInfo[] { new VariableInfo("memb","String",true,VariableInfo.AT_END) }; } } When we use AT_END we will get the same error as before The scope of a variable decides where the variable will be created and where it will be allowed. Our next few examples will further expand on this concept. d9.jsp <%@ taglib uri="vijay" prefix="pp" %>

• <%= memb %>

ea.tld 1.0 <shortname>pp log1 examples.xxx examples.yyy JSP att1 <required>true

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att2 <required>true att3 <required>true xxx.java package examples; import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; import java.util.Hashtable; import java.io.Writer; import java.io.IOException; public class xxx extends ExampleTagBase implements BodyTag { private String atts[] = new String[3]; int i = 0; public void setAtt1(String value) { System.out.println("setAtt1 " + value); atts[0] = value; } public void setAtt2(String value) { System.out.println("setAtt2 " + value); atts[1] = value; } public void setAtt3(String value) { System.out.println("setAtt3 " + value); atts[2] = value; } public int doStartTag() throws JspException { System.out.println("doStartTag "); return EVAL_BODY_TAG; } public void doInitBody() throws JspException { System.out.println("doInitBody "); pageContext.setAttribute("memb", atts[i]); i++; } public int doAfterBody() throws JspException { http://www.vijaymukhi.com/documents/books/javajsp/chap10.html (29 of 31) [5/2/2008 11:00:33 PM]

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System.out.println("doAfterBody " + i); try { if (i == 3) { bodyOut.writeOut(bodyOut.getEnclosingWriter()); return SKIP_BODY; } else pageContext.setAttribute("memb", atts[i]); i++; return EVAL_BODY_TAG; } catch (IOException ex) { throw new JspTagException(ex.toString()); } } } yyy.java package examples; import javax.servlet.jsp.tagext.*; public class yyy extends TagExtraInfo { public VariableInfo[] getVariableInfo(TagData data) { return new VariableInfo[] { new VariableInfo("memb","String",true,VariableInfo.AT_BEGIN) }; } } Output in Browser Window * 98.5 * 92.3 * 107.7 Lets sum up everything now. Nearly everything remains the same. At first, let's take a look at the jsp file. As usual we have tags like html and then body. Here log1 has a prefix pp and it has three attributes; att1, att2 and att3 with values 98.5, 92.3 and 107.7 respectively. The

tag is to display an unordered list and it needs
• which stands for the start of the list and
means the end of the list. These tags i.e. ul and li are only meant for ornamental purposes. Memb is a variable which is enclosed in % and angle brackets i.e. it is a jsp tag. As we have memb and 3 attributes, we should change the tld file to include these attributes. The attributes and methods have the first preference. Hence the setAtt1, setAtt2 and setAtt3 functions will be called first. These three functions accept only one string parameter. We have created an array atts of type String. In these functions, we are initializing the array atts to the values passed on to the Java program by jsp. Since this is done first, before any other function is called, you will see setAtt1, setAtt2 and setAtt3 with their values

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displayed using System.out.println in you server dos screen. Once this is done, the next function to be called is doStartTag. This function displays 'doStartTag' and then we return EVAL_BODY_TAG. It is because of this return value that the JSP Engine now calls doInitBody. In this function, the value of i is 0 and we then call pageContext.setAttribute. This creates memb as a variable and initializes it to the value stored in atts[0]. The value of i is incremented by 1 and the next function to be called is doAfterBody. Here, we check whether the value of i equals 3. As this condition evaluates to false, the else is called. Now pageContext.setAttribute will initialize memb to the value in atts[1]. Again the value of i is incremented but now we return EVAL_BODY_TAG. This will call doAfterBody once again and since the if condition is false again, it will initialize memb to the value in atts[2]. On adding 1 to i, ii now becomes 3. EVAL_BODY_TAG will call doAfterBody once again. Now the value of i is 3, so the function bodyOut.writeOut(bodyOut.getEnclosingWriter()) will write these values of memb on the browser screen and return SKIP_BODY. Thus it will now skip the body functions. In this example, comment out the i++ and then see the results. Remove the comments and you will understand the flow of doAfterBody.

Contents | Foreword | About the Authors | Introduction | Appendix |Chapter 1 |Chapter 2 |Chapter 3 |Chapter 4 |Chapter 5 |Chapter 6 | Chapter 7 |Chapter 8 |Chapter 9 |Chapter 10 |Chapter 11

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11. JAVA FOUNDATION CLASSES All mothers of the world love to boast about their new babies to the entire world. Oh, what a sweet child I have! At such a tender age, my child can do so many things! No other baby is as good looking as my own! And they would go on and on. It was the same story when, about five years ago, Sun Microsystems told us about their new baby, whom they had named Java. Java, they told us, was better than anything, anyone in the software industry had ever produced. The things it could do were absolutely incredible. Why, it could even work on any platform! Have you ever heard of anything like it before? Write a program once and it would work anywhere. And ofcourse, nothing looked as beautiful as Java. We were hooked! We had heard other mothers boast about their babies but this seemed different. We fell in love with Sun's baby for the promise it held of ushering in a new paradigm in the world of Information technology. That promise, alas, remained just a promise. Our relationship with Java turned into one with many ups and downs, with more downs than ups. Simply because we realised there really wasn't a lot that we could do with Java. And as far as the looks department was concerned, well, Cindy Crawford wasn't about to feel threatened by Java. And that's probably one hell of an understatement. Because we actually thought that the output we got from Java looked quite ordinary. We felt let down. But all that was before the Java Foundation Classes or the JFCs were released. When we first heard Sun talk about the JFCs, we wondered whether the people at Sun were referring to Jokes For Crossplatform workability. To tell you the truth, earlier, we had been so disappointed with Java that we defected to MicroSoft's ActiveX. We spent more than a year going ga-ga about the brilliant features of ActiveX. It not only looked good but also could actually do really great things. No longer. We are back home to where we belong. With Java. Infact, had Java been like this since the beginning, we would have never gone astray. So let's move onto looking at a couple of programs in the JFCs. We hope that you will be convinced that this is definitely where our world is going to be heading. program 0 zzz.java import java.applet.*; import java.awt.*; public class zzz extends Applet { public void init() { Button b; b = new Button("Hi"); add (b); http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (1 of 25) [5/2/2008 11:01:22 PM]

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} } If you do not understand this program, then refer to the chapter titled 'Shlurrp Java'. We compile this program using javac and then using Appletviewer we open a.html to run this file. a.html All that this program does is place a Button on our screen,which says 'Hi', This is the type of output we get when we use the original JDK1.x. Not very impressive. Which is why we called this program 0. Another word for useless or dull. Time to get to the real thing. zzz.java import java.applet.*; import java.awt.*; public class zzz extends Applet { public void init() { JButton b; b = new JButton("Hi"); add (b); } } In our first program, we have merely added a 'J' in front of Button to get the term JButton. Now when we say 'JButton b; ', we are merely informing the compiler that b looks like a JButton. Which means that it has all the properties and attributes of a JButton. We haven't as yet created a JButton in our program. To do that, we have to actually say that b=new JButton() or call a function that returns an object that looks like a JButton. When we compile this program using the javac compiler, we get an error message that says 'class JButton not found in type declaration'. >javac zzz.java zzz.java:7: Class JButton not found. JButton b; ^ zzz.java:8: Class JButton not found. b = new JButton("Hi"); http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (2 of 25) [5/2/2008 11:01:22 PM]

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There's a simple reason for this error. If you told me on the phone that your name is Bill, I wouldn't know who you were. Bill Clinton? Bill Gates? Billy The Kid? I wouldn't know until you told me your full name. I'd probably slam the phone down. But don't get depressed so soon. Precisely, what the compiler is doing right now is saying 'give me your full name or else how am I to know who you are?'.Write this full name and the compiler should be able to recognize you. However an easier method of doing things is to write the statement import javax.swing.*; The terms after the word 'import' and before the '*' will automatically become a prefix to JButton whenever needed. This is shown in the next program . zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { JButton b; b = new JButton("Hi"); add (b); } } You mean we went through that much trouble just to get something that looked as bad as the best that JDK1.x could offer. Oh no! That's why we ran away from java in the first place! And what about all those terms we kept on hearing about like ModelViewController, delegates, etc? Things that were supposed to make java better looking? In case you are wondering whether to go further in this chapter, let me assure you that we shall get to all those terms at a relaxed pace. You probably won't even realise that we have run programs using 'delegates', 'MVC', etc, until we actually point out to you that you have. And we solemnly promise to create better looking buttons in the future. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (3 of 25) [5/2/2008 11:01:22 PM]

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JButton b; ImageIcon i; i = new ImageIcon("buttonImage3.gif"); b = new JButton(i); add (b); } } Before you run this program within your java subdirectory, move to demo\jfc\swingset\images and copy all the 'gif' files into your current directory. A .gif file merely contains an image. In this program we have the term ImageIcon. ImageIcon is an object that stands for an image. We can use any .gif file but right now we are using the files that Sun has given us. When we run this program, we see a button resembling a round circle with a bright green arrow in the centre. If you had worked with java earlier, you would have realised that this button looks a lot better than what buttons used to look like. And all that we have done is to create an ImageIcon using our .gif file and adding this ImageIcon to our button. The image contained in buttonImage3.gif file is pasted on to our button. Earlier when we used button, all we could do was add text to it. Now in addition to plain text, we can also add images to our buttons. In the good old days, if we wanted to paste on images using java all we could do was to sit on our heads in some yoga style and meditate, waiting for the JFCs to be released. But, right now, we can stop meditating because the JFCs are here, and we have work to do. This is probably an easier way to paste an image onto the a button than when using the JFCs. That's also one of the major reasons why we have come back to Java. It's so simple to learn and work with. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { JButton b; ImageIcon i , j; i = new ImageIcon ("buttonImage3.gif"); j = new ImageIcon ("duke2.gif"); b = new JButton (i); b.setPressedIcon (j); add (b); } }

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In this program, we have created two ImageIcons. The only thing new in this program is the line b.setPressedIcon(j). Here, we obviously mean that 'setPressedIcon' is a function in JButton. When we run our program, we see our image, namely 'buttonImage3.gif' on our button, as in our previous program. Now, due to this statement, when we keep the mouse depressed on our button, the first image is replaced by the second. So as long as we keep the mouse depressed, we see the image of a duke with a funny hat. When we release the mouse, we once again see our original image, that is in buttonImage3.gif. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { JButton b; ImageIcon i , j; i = new ImageIcon ("buttonImage3.gif"); j = new ImageIcon ("duke2.gif"); b = new JButton (i); b.setRolloverIcon (j); add (b); } } This program is similar to the previous program, where we have two ImageIcons and want to replace one with the other. By now, however, we must have become pretty lazy. I mean, why take all the trouble to click on our JButton and keep it depressed to change the image, when we can achieve our objective by merely positioning the mouse over our JButton? Fortunately, we have some thing just for you . Something called setRolloverIcon( ) . So execute this program and just place the mouse over the Button. You will notice the change immediately. The first image has been replaced by the second. Move the mouse away from our JButton, and once again, we see the original image. A point to be remembered here is that when we say b.setRolloverIcon( ) ,we obviously mean that the function setRolloverIcon is part of JButton. This may, however, not be the case, as JButton itself may be derived from something else which contains this particular function. Don't worry about this right now, as we shall be covering all this in greater detail later on. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (5 of 25) [5/2/2008 11:01:22 PM]

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{ public void init() { JButton b; ImageIcon i , j; i = new ImageIcon ("buttonImage3.gif"); j = new ImageIcon ("duke2.gif"); b = new JButton (i); b.setEnabled (false); b.setDisabledIcon (j); add (b); } } In Java, most components, like JButtons, JCheckboxes,etc are all derived from the class, JComponent. They therefore, can make use of all the functions of JComponent. One of these is the function setEnabled(). This function requires a boolean as a parameter. When we say b.setEnabled(false), all that we are doing is disabling b, which is our JButton. The next line b.setDisabledIcon(j) simply says that when b has been disabled, replace the first ImageIcon with the one in 'j'. When we execute this program, we don't see the first image at all, as the button has been disabled immediately on execution. We directly get to see the second image. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { JButton b; b = new JButton ("Hello"); Font f=new Font ("Dialog",Font.BOLD,24); b.setFont (f); add (b); } } Maybe, we do not like the look of the text that we have placed in our JButton. Or maybe we just want to increase the size of the text to make it more prominent. All we have to do is to change the font. We first create an object that looks like a Font. While doing this, we have to give it three parameters. The first is the name of the font. The second refers to the properties of the http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (6 of 25) [5/2/2008 11:01:22 PM]

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font, that is, whether the font is bold, italic, or underline or strikethrough. And finally we give the point size. We should know that 72 points make an inch. JButton has a function setFont( ) to set a particular font for whatever we have written. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { JButton b; b = new JButton ("Hello"); b.add(Box.createRigidArea(new Dimension (100,50))); add (b); } } Sometimes, we might have too many buttons on a screen and they might appear too close to each other. To avoid any cluttering of buttons, we need to separate our buttons. Box is a static object. It has a static function called createRigidArea ( ). Due to this function, our JButton will now be allocated some area on the screen. Of course, we still have to specify how large we want this area to be. For this, we have to pass a Dimension function to it, which contains the width and the the height . Once we have created this area around our box, nothing else besides our JButton can occupy this area. Any new component will now be placed outside this area. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { JCheckBox b; b = new JCheckBox("hi"); add (b); } } Now that we have done JButtons, we shall realize that JCheckBoxes are almost exactly the same thing,except for the fact that the borders around a checkbox aren't clearly visible. Compared to earlier checkboxes in Java, we can now add an ImageIcon to our JCheckBoxes. zzz.java http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (7 of 25) [5/2/2008 11:01:22 PM]

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import java.applet.*; import java.awt.*; import java. awt.event.*; import javax.swing.*; public class zzz extends Applet { public void init() { JCheckBox b; ImageIcon a = new ImageIcon ("buttonImage3.gif"); b = new JCheckBox(a); b.addItemListener (this); add (b); } } It is not sufficient to merely place a checkbox on our screen. When we click on our checkbox, we want to know if we have actually clicked or not. We may find out whether we have clicked by making use of the function addItemListener (), within which we pass the parameter 'this'. When we compile our program, we get some strange error message that says 'Incompatible type for method. Explicit cast needed...'. The parameter 'this' refers to our current object. In our case, the current object is zzz as well as Applet. The function addItemListener however, demands that it requires an object that is an ItemListener. This is now shown in the next program. zzz.java import java.applet.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class zzz extends Applet implements ItemListener { public void init() { JCheckBox b; ImageIcon a = new ImageIcon ("buttonImage3.gif"); b = new JCheckBox(a); b.addItemListener(this); add (b); } } In this program we have to make sure that our current object is an ItemListener. ItemListener http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (8 of 25) [5/2/2008 11:01:22 PM]

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is an interface so we use the term 'implements' to append ItemListener to our class. Now 'this' in addItemListener( ) refers to zzz, Applet as well as ItemListener. On compilation, we still get an error which tells us that we do not have some abstract function. This is because when we say 'implements ', we can be sure that whatever follows this term is an Interface. Within an Interface, all the functions are Virtual functions. These functions do not contain any code. To remove the errors in our program, all we have to do is to add these functions to the class that implements the interface. When we say our class extends another class, we mean that our class contains all the code that was present in the base class, but when we say that our class implements an interface, it means that our class will now contain all the functions that are present in the interface. The interface in our program, namely ItemListener, has only one virtual function 'itemStateChanged( )', which we have added in our next program. zzz.java import java.applet.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class zzz extends Applet implements ItemListener { public void init() { JCheckBox b; ImageIcon a = new ImageIcon ("buttonImage3.gif"); b = new JCheckBox(a); b.addItemListener(this); add (b); } public void itemStateChanged(ItemEvent e) { System.out.println("function called"); } } When we now compile the program all the errors disappear, confirming that there is only one virtual function in ItemListener. As we said earlier, the only prerequisite is that the function must be present within our class. Within this function, we may add any code that we may want. Here, we have placed the statement System.out.println( ). When this function gets executed, whatever text we have written within the function appears at our dos prompt, for the number of times that we have clicked on our JCheckBox. System, by the way, is a static object. What we mean by that term is that we don't have to say 'new' to make use of it. At this point, we must realise that we may have more than one checkbox in our program, which may also call itemStateChanged. To distinguish between different components calling this function,we use ItemEvent. We also note that addItemListener is one of the new concepts of http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (9 of 25) [5/2/2008 11:01:22 PM]

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jdk1.x. Earlier, when we wanted to call a function we had to use handleEvent. Here, things have been made much simpler, as we can now call our own code. zzz.java import java.applet.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class zzz extends Applet implements ActionListener { public void init() { JButton b; ImageIcon a = new ImageIcon ("buttonImage3.gif"); b = new JButton(a); b.addActionListener(this); add (b); } public void actionPerformed(ActionEvent e) { System.out.println("function called"); } } An ItemListener is essentially meant for a JCheckbox. When we are working with buttons, we would rather use an Action Listener. This Interface, as well, has only one virtual function which we have to add within our class which implements ActionListener. This function is called actionPerformed. Also we use ActionEvent to distinguish between different JButtons. Now every time we click on JButton, our code which is in actionPerformed is called. This is how we handle events in the Java Foundation Classes. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { JLabel l=new JLabel("hi"); add( l); } }

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If we want to print any text on to our screen, we normally make use of a label. Here we use JLabel. The size of the label will vary according to the size of the text we have placed into it. Here, we have only written the word 'hi'. Short and sweet. This now appears at the top of our applet in the centre. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { ImageIcon i=new ImageIcon("buttonImage3.gif"); JLabel l=new JLabel("hi"); l.setIcon( i); add( l); } } A JLabel, as with everything else in the JFCs, can have two entities within it. What we mean to say is that within a JLabel, we can have an image as well as some text, both of which may be independent of each other. Here, when we created our JLabel, we associated a text 'hi' with it. We also create an ImageIcon. Every JLabel has a function setIcon( ). We place our Image Icon within this function. When we execute this program, our label now contains an image as well as the text, side by side. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { setLayout(new BorderLayout()); ImageIcon i = new ImageIcon ("BigTiger.gif"); JLabel l=new JLabel(i); add(l); } } In this program, we have created an ImageIcon as we had done earlier. We have added this ImageIcon to a JLabel. This JLabel has now been added to our screen. We have also created http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (11 of 25) [5/2/2008 11:01:22 PM]

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the simplest of borders for our applet when we said setLayout(new BorderLayout( )). The difference, in this program, is that the image we have in our .gif file is of a size much larger than any image that we have used before. When we run this program, if we get the feeling that we aren't really getting to see the entire image, we might probably just be right. Even if we increase the size of our applet to it's full size, we may still not see the full image. After all, the image in this .gif is probably larger than even our entire screen. Wouldn't it be great if we could just scroll through the image, just as we use a scrollbar to view a large text document ? Well, we are trying to do just that in our next program. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { setLayout(new BorderLayout()); add("Center",new yyy()); } } class yyy extends JScrollPane { public yyy() { ImageIcon i = new ImageIcon ("BigTiger.gif"); JLabel l=new JLabel(i); add(l); } }

We create a new class which can now extend the particular class that we require, namely JScrollPane. JScrollPane contains functions that will enable us to create scrollbars within our Applet. We call the constructor of this class when we say new yyy( ), from init( ). However, when we now run this program, we find that only the border has been formed within our applet. We don't get any image unlike in one of the earlier programs , here we at least got to see half the image. We rectify this problem in the next program. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (12 of 25) [5/2/2008 11:01:22 PM]

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public class zzz extends Applet { public void init() { setLayout(new BorderLayout()); add("Center",new yyy()); } } class yyy extends JScrollPane { public yyy() { ImageIcon i = new ImageIcon ("BigTiger.gif"); JLabel l=new JLabel(i); getViewport().add(l); } } All that we have done out here is to write getViewport( ).add( l ) instead of just add( l ). Here, we are saying that getViewport() is a function within JScrollPane which ensures that scrollbars appear within our applet when we call the function add() from it. When we have an image that is too large to fit onto our screen, we need to create a smaller window to enable us to view just a portion of the image. This is done by getViewport(). If we now use the scrollbar, we may see another part of the image. All this assumes that the image within our gif file is large enough, otherwise we shall not see any scrollbars. zzz.java import java.applet.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class zzz extends Applet implements ActionListener { JProgressBar p; public void init() { JButton b; b=new JButton("click"); p=new JProgressBar(); b.addActionListener(this); p.setMinimum( 0); p.setMaximum( 100); http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (13 of 25) [5/2/2008 11:01:22 PM]

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p.setValue( 10); add( b); add( p); } public void actionPerformed( ActionEvent e) { int i=p.getValue()+10; p.setValue( i); System.out.println("hi"); } } Whenever software is in the process of being installed onto our computer, we see a progress bar which tells us how much of the process has been completed. The problem with most progressbars we have seen to date is that they are never accurate. Sometimes the pointer of the progress bar will move slowly in the beginning and then in a flash of a second, will reach the end. At other times, it moves quite fast, but stops just before the end of the bar for a time period that seems like infinity. Anyway, let's see how the Java Foundation Classes have implemented progressbars. We have added an ActionListener to the button in our program. The bare minimum information we need to give our progressbar are the values at the extreme left end and the extreme right end of the progressbar. For this we have two functions, setMinimum() and setMaximum() respectively in JProgressBar. The function setValue() tells the pointer of the progress bar where it should start from when it first starts executing. Here we have placed the initial position at 10 using this function. Whenever we click on the button, the current value of the progress bar is obtained by the function getValue(). We add 10 to this value, and place it in a variable i. The current value of the progressbar is now set to the the value in variable i. Thus each time we click on the button we increment the value of the progressbar by 10. When we click on the button for the first time, the initial value is 10, which is now incremented by 10 to become 20. The pointer of the progressbar now points to this value. In a practical progressbar, we may use something else besides a button to use the progressbar's pointer to increment by a fixed amount, but the concept remains the same. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends Applet { public void init() { setLayout(new BorderLayout()); http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (14 of 25) [5/2/2008 11:01:22 PM]

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add("Center",new sss()); } } class sss extends JPanel { public sss() { JSlider s; this.setLayout(new BorderLayout()); s=new JSlider(JSlider.HORIZONTAL,100,1000,400); s.setPaintTicks(true); s.setMajorTickSpacing(20); this.add(s); } } If you look at any music system, you'll notice that you can adjust the volume or the bass and other functions using a slider. A slider is normally used when we have a wide range of values and we want to choose a value within that range without typing in that value. When we have a sliderpanel, all we do is to move the slider to the required value. Earlier, it was almost impossible to obtain a slider in Java. In contrast, Windows allowed us to create a slider with great ease. Now, using the JFCs, this is possible in Java as well. We first create an object that looks like a JSlider. We have specified that it's alignment is horizontal. As we had done earlier with our progressbar, we specify the minimum and maximum values of the slider, as well as the value we want it to be set at initially. If we just write only the first three lines within the constructor and then say add(s), we shall obtain a slider which we can drag with a mouse from one end to another. The only problem is that we shall have difficulty placing the slider at any particular value we want it at. For this, we enable markers between the two ends. We also specify how much space should be there between each marker, using the function setMajorTickSpacing(). Around our slider, we also want a border with some title. So, here, we have put a border that looks like JTitledBorder(), with two parameters: s refers to our slider around which we want our titled border and the second parameter now becomes the title of our slider. If we say this.add() or this.setLayout(new BorderLayout()), 'this' merely refers to the current class we are in. It doesn't make a difference if we do no write 'this' before add(). zzz.java import java.applet.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.event.*; public class zzz extends Applet { http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (15 of 25) [5/2/2008 11:01:22 PM]

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public void init() { setLayout(new BorderLayout()); add("Center",new sss()); } } class sss extends JPanel implements ChangeListener { JLabel tf; public sss() { JSlider s; setLayout(new BorderLayout()); tf=new JLabel("Slider value: "); add("South",tf); s=new JSlider(JSlider.HORIZONTAL,100,1000,400); s.setPaintTicks(true); s.setMajorTickSpacing(20); s.addChangeListener(this); this.add(s); } public void stateChanged(ChangeEvent e) { JSlider s1 =(JSlider) e.getSource(); tf.setText("Slider Value: "+s1.getValue()); } } It's not possible for us to be totally satisfied by merely moving the slider from one end to another. We would also like to know the current position of the slider. To do this , we have created another JLabel and placed it in the south. Now all user interface tools have a listener associated with them. A slider has a ChangeListener. Here we have written s.addChangeListener(). The 'this' merely specifies that ChangeListener which is an interface is in in the very same class. We have a function called StateChange within Change Listener which will get called each time we move the slider up and down. We have a parameter that looks like ChangeEvent that would allow us to distinguish between different sliders calling the function stateChanged (). But right now we have only one slider so that is not important. Here e.getSource will return the object that calls stateChanged(). In this case, we know that it is a JSlider, so that is what we are casting it to. The getValue() function will tell you the current position of the slider. Now setText() will allow this value to be seen on our label at runtime.

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zzz.java import java.applet.*; import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.lang.*; public class zzz extends Applet { public void init() { JButton b=new JButton("Hello, how are you"); add(b); DebugGraphics.setFlashTime(10); b.setDebugGraphicsOptions(DebugGraphics.FLASH_OPTION); } } To deal with problems that we may encounter with any graphics application in java, we have a static object named DebugGraphics. This static object has a function named setFlashTime(). Our image will be drawn on screen within a time duration that depends on the value we pass to this function. In the next statement, we have said setDebugGraphicsOptions(DebugGraphics.FLASH_OPTION); where FLASH_OPTION is another static variable in DebugGraphics. Each time a paint message comes, this is the function that will cause our image to be redrawn. Since we are redrawing our image very slowly, we can see, at what point in time, any errors in the drawing of the image, occur. In this program, we have only used DebugGraphics to check whether a button is being drawn properly. Normally, it is used for debugging complicated objects on screen when we want to see in slow motion what is happening at every stage. We could try this function with another component, or a User Interface. zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends JPanel { static JFrame frame; public static void main(String s[ ]) { frame = new JFrame("zzz"); frame.getContentPane().add("Center", new zzz()); frame.pack(); http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (17 of 25) [5/2/2008 11:01:22 PM]

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frame.setVisible(true); } } We now get down to working with applications in java. When we run such an application, we don't use appletviewer, but instead say java zzz. All the programs that we shall be doing after this will be applications and not applets. In an application, the first function to be called is always main(). The reason we have made main public is because we want every one to be able to access it. The function main() gets an array of strings, which are the parameters we may pass after the name of the program. We create a JFrame with the title zzz. In this frame, we put all things together using the function pack(). Without setVisible( true), we shall not be able to see anything. Notice that we have declared frame to be of type static JFrame. We have to declare it as static to be able to use it in another function, in this case main(). Alternately, we could have put this statement within the function main(), in which case, we may avoid the use of the term static.To learn more about applications in java, refer to one of the earlier chapters . zzz.java import java.applet.*; import java.awt.*; import javax.swing.*; public class zzz extends JPanel { public zzz() { JRadioButton b; b=new JRadioButton("hello"); add("Center",b); } public static void main(String s[]) { JFrame f = new JFrame("hi"); f.getContentPane().add(new zzz()); f.pack(); f.setVisible(true); } } A radiobutton functions in a manner similar to that of an ordinary button or a checkbox, only it

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is smaller and round in appearance. Each and everyone of these components have a function setKeyAccelerator(). Now when we write o in single quotes within this function, and now execute this program, we shall notice that the first occurance of the letter we have placed within this function is now underlined. If we now press the Alt key as well as the letter o, our radio button which contains this text is activated. The function setKeyAccelerator() enables Sun to implement, in part, a very crucial concept of almost all computers used today. A concept that says that even if our mouse is not working properly, we must be able to operate our computer using a keyboard. This is something of a standard across platforms and Sun has made it very clear that we shall be able to use the Java Foundation Classes using only a keyboard, without using a mouse. { Have you ever wondered what happens to a Mac user when his mouse is giving him problems ? Don't even ask ! zzz.java import java.applet.Applet; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class zzz extends JPanel { static JFrame frame; public zzz() { JMenuBar m = new JMenuBar(); JMenu f = new JMenu ("File"); f.setIcon(new ImageIcon("folder.gif")); m.add(f); m.validate(); add(m); } public static void main(String s[ ]) { frame = new JFrame("zzz"); frame.getContentPane().add("Center", new zzz()); frame.pack(); frame.setVisible(true); } } As we said earlier, the first function to be called in an application is main(). When we say new zzz(), we are calling the constructor of the function zzz. Here, we have created a menubar called m of type JMenuBar. Now to this menubar we are going to add our menus. Our first menu has been called f and has a text 'File' associated with it. Also in this menu, we have created an ImageIcon, which we add to our menu. When we say validate(), what we are doing is forcing the menubar to redraw itself. http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (19 of 25) [5/2/2008 11:01:22 PM]

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zzz.java import java.applet.Applet; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class zzz extends JPanel { static JFrame frame; public zzz() { JMenuBar m = new JMenuBar(); JMenu f = new JMenu ("File"); f.setIcon(new ImageIcon("folder.gif")); f.setHorizontalTextPosition(JButton.RIGHT); JMenuItem o=new JMenuItem("Open",new ImageIcon("open.gif")); o.setHorizontalTextPosition(JButton.RIGHT); f.add(o); m.add(f); JMenu gg = new JMenu ("Color"); gg.setHorizontalTextPosition(JButton.RIGHT); JMenuItem red=new JMenuItem("Red"); gg.add(red); red.setHorizontalTextPosition(JButton.RIGHT); JMenuItem blue=new JMenuItem("Blue"); gg.add(blue); blue.setHorizontalTextPosition(JButton.RIGHT); m.add(gg); m.validate(); add(m); } public static void main(String s[ ]) { frame = new JFrame("hi"); frame.getContentPane().add("Center", new zzz()); frame.pack(); frame.setVisible(true); } } While doing these programs, we have to remember the heirarchy of the terms involved. At the top of this heirachy is the menubar. The menubar has to be filled with menus. There may be a number of menus within a menubar and they will all appear in the same line on the screen. http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (20 of 25) [5/2/2008 11:01:22 PM]

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Each menu may have a number of menu items which appear just below the menu, when we click on the menu. Here, a single menuitem called 'Open' is added to our first menu, 'File'. For our second menu 'Color', we have added two menuitems, namely red and blue. The entire procedure is the same as in the previous program. zzz.java import java.applet.Applet; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class zzz extends JPanel { static JFrame frame; public zzz() { JMenuBar m = new JMenuBar(); JMenu f = new JMenu ("File"); f.setIcon(new ImageIcon("folder.gif")); f.setHorizontalTextPosition(JButton.RIGHT); JMenuItem o=new JMenuItem("Open",new ImageIcon("open.gif")); o.setHorizontalTextPosition(JButton.RIGHT); f.add(o); JMenuItem e=new JMenuItem("Exit"); e.setHorizontalTextPosition(JButton.RIGHT); f.add(e); e.addActionListener(new aa()); m.add(f); add(m); } public static void main(String s[ ]) { frame = new JFrame("hi"); frame.getContentPane().add("Center", new zzz()); frame.pack(); frame.setVisible(true); } } class aa implements ActionListener { public void actionPerformed(ActionEvent e) { System.exit(0); } }

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As usual, we have a menubar to which we add menus. The menus themselves may consist of a number of menuitems. Until now, we have been only displaying these menuitems. Wouldn't it be useful if we were able to click on a menuitem and perform some task. For this, we shall obviously need an ActionListener. With our menuitem 'Exit', we say addActionListener (new aa()). aa has to implement ActionListener. This interface has one function, actionPerformed(), which contains the code System.exit(0). This results in us getting out of this application. We could, instead, have performed some other useful task using this function, with this type of an application. Listboxes are the kind of examples that we were talking a lot about. In the previos program we only displayed numbers. However we have always said that the nice thing about the Java Foundation Classes is that where ever we display numbers ,we may also display pictures. Now, listbox has a function named setCellRenderer. Here, the statement, new te (), will obviously call the constructor of class te. Within the class te, all that we have done is a series of initialisations. Now te has to look like Renderer. Therefore we have said te implements Renderer. Renderer have two virtual functions. One is setValue () and the other is getComponent (). The first function to get called is getComponent(). The return value of getComponent() is of type Component. When we say 'return this', it means that it can return either a te or a JLabel or a Renderer. But here since we can return only a component, we return a JLabel. Now, setValue() gets called. Here, the Object is what we have returned in the function getComponent(), namely our JLabel. It is, however, not useful to us, as far as processing data is concerned, if the object is a component. This is why we are casting it to an Integer. The class Integer has a function, intValue(), which will return the object's value. . Therefore i will now have the current value of the item or cell within the listbox. The boolean parameter is used to find out whether we have selected that particular item or not. In case it has been selected, we also print the price along with the picture, otherwise we only display the picture. The actual displaying of the picture within each cell is done by setIcon(). We have to call our renderer each time a cell has to be painted, which is why we may notice setValue() and getComponent() being called a number of times from whatever System.out.println() displays out at our DOS prompt. Assume we are using an Operating System like Windows and we are in the main Window. Take a case where a part of this window is overwritten by another window. At this point in time, Windows will claim that it is not its responsibility to draw whatever is in that window. Suppose we finish our work in the second window and if we come back to our original window. Then the Windows operating system will tell our window that a part of it has been dirtied. Therefore our window needs to be repainted. Windows does this by sending our window a paint message. Suppose we had some text on our screen. A part of this text was in the section that had been overwritten. Now we have to rewrite the text using the Windows SDK command TextOut. This command has to be given within the function paint. Windows is a very smart operating system and knows how to optimise time. This is, I suppose, for people who are forced to run Windows on 486s, but it does save on time when a number of complex items have http://www.vijaymukhi.com/documents/books/javajsp/chap11.html (22 of 25) [5/2/2008 11:01:22 PM]

Java-Servlets-JSP

to be redrawn. Getting back to our textout command in paint, the complete text is not rewriiten. Only the part of the text that had been overwritten is now redrawn. Notice that we have said 'redrawn' and not 'rewritten'. As far as Windows is concerned, it treats everything that has to go on to screen as a series of pixels. Therefore, text as well as images are treated the same way. There are a few new things that the java foundation classes have provided us that make our applets or applications better looking. Not only that, the way our applets look, can be changed, depending on what the user wants it to look like. Take for instance the case of a button. People who use Windows will want a button that looks like a Windows button, while a person who is used to a Macintosh will want the same button to be in the Mac style. This poses a dilemma. Should we keep the button looking the same irrespective of the Operating System or should the button have the look and feel of the particular operating System it is running under. The JDK1.0 used the second option and what it did was to have the button drawn by the operating system itself. There was one problem with this approach. Suppose you had earlier worked on an application on the Mac, and now you switched on to say an Intel machine with Windows on it. You will realise that the same application looks very different under your new operating system. So what the JFCs decided to do was a very simple thing. They gave the user the option of changing the look and feel. This was a very smart thing to do. After all, when we go to work, our dress is very formal. However, if we have to attend a party with friends, we won't go wearing the same clothes. We would rather change in to jeans and T-shirts. Something similar can be done with the JFCs. If our application is running under Windows, but if we do not like it's look and feel, we may change it to another look and feel that is either supplied by Sun or has been created by us. This option is available to us at runtime, and enables us to decide how our application will be displayed. Earlier, if we were using Windows, we didn't have an option as to how our application would be displayed. Windows itself decided how it would be displayed. Now with the JFCs we have a very flexible look and feel. We call this the Plugable Look and Feel. The Java Foundation Classes has the ability to change the look and feel of a component, according to what the user desires. To achieve this change in the user interface, we make use of a static object called UIManager. This has a static function called setLookAndFeel(). This will set the look and feel within our frame, to whatever we have specified. There are classes which refers to a Windows, Motif look and feel. Hence when we run the program, we see the objects displayed as per the platform we have selected. You can have these components show a neutral look too. Now we come to the concept of 100% Pure Java. Right now we are using the JDK1.2.2 but underneath it all, is the JDK1.2. All that JDK1.2.2 did was to call code. This code if it had to run under Windows would have to be in a DLL. So that is where we call it from. This may

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further call code in other Windows DLLs which will finally call code in VxDs. Now when we say 100% Pure Java, we mean that our JFCs are basically .class files that are executed. In none of these .class files do we call native code. In other words, we do not call any 'C' code. We can however call code from the JDK1.2 which in turn may call native code. But the JFCs remain 100% Pure Java.

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Contents | Foreword | About the Authors | Introduction | Appendix |Chapter 1 |Chapter 2 |Chapter 3 |Chapter 4 |Chapter 5 |Chapter 6 | Chapter 7 |Chapter 8 |Chapter 9 |Chapter 10 |Chapter 11

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