Jsp Element

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Java Server Pages Technology

JSP Technology 

Objectives 

Write the opening and closing tags for the following JSP tag types    

Directives Declaration Scriplet Expression

JSP Technology 

Identify JSP Life cycle       

Page translation JSP page compilation Load class Create instance Call jspInit Call _jspService Call jspDestroy

JSP Technology 

Identify page Directive attribute and its value    

Import a java class into JSP page Declare that a JSP page exists within a session Declare that a JSP page uses an error page Declare that a JSP page is an error page

JSP Technology 

JSP Syntax ELEMENTS  Just like any other language,the JSP scripting language has well defined grammar and includes syntax element for performing various tasks,such as declaring variables and methods, writing expression and calling other JSP page.

JSP Technology 

JSP elements Types      

Directive Declaration Scriptlet Expressions Action Comment

JSP Technology

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JSP Directives  

Provide global information about a particular JSP page Can be of three types: page, include, and taglib.

JSP Technology 

Page directive:  

Notifies about the general settings of a JSP page Attributes include:  contentType: To specify the MIME type of the response  extends: To specify the name of the parent class  errorPage: To specify the URL of a JSP page used to trap errors

JSP Technology 

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isErrorPage (Boolean attribute): To specify if a JSP can be used as an error page import: To specify the names of the packages available for a JSP page language: To specify the scripting language session: To specify the availability of session data for a JSP page. buffer:Specifies the size of the output buffer. If buffer size is specified it must be specified in kilobytes. autoFlush: A boolean literal indicating whether the buffer should be flushed when it is full. isThreadSafe:A boolean value indicating whether the JSP page is thread safe.

JSP Technology 

Include directive: Used to specify the name of the files (in the form of their relative URL) to be inserted while compiling the JSP page  Contents of the inserted files become part of the JSP page  Also used to insert a part of the code common to multiple pages Example: <%@ include=”bnkHeader.html” %>  About taglib directive we will learn in custom tags. 

JSP Technology 

Declaration  Declaration declare and define variables and methods that can be used in the JSP page.  Syntax:  <%!=%>  Example

<%! int i=0; int j=0; int z=0; int prod=0; %>

JSP Technology 

Note:  Instance variables are automatically initialized to their default value, while local variable must be initialized explicitly before they are used.  Instance variable are created and initialized only once. Thus variable declared in JSP declaration retain their values across multiple requests.  Local variables are created and destroy for every request.

JSP Technology 

Scriplets Consists of valid code snippets enclosed within the <% and %> JSP tags Example: 

To accept the user name and display the name 10 times: <%@ page import="java.util.*" %> <%@ page language="java" %>

JSP Technology <% String name=(request.getParameter("t1")); out.println(""); out.println(""); out.println("

A Scriplet example

"); for(int i=0;i< 10;i++) { out.println("
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JSP Technology out.println(" Hello" + " " + name + " " + "Count" + i ); } out.println(""); out.println(""); %>

JSP Technology 

JSP Expressions 

Used to directly insert values into the output

Example: <%=msg%>

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JSP Actions  Used to perform tasks such as:  insertion of files  reusing beans  forwarding a user to another page  instantiating objects

JSP Technology 

Include actions such as: 

<jsp:useBean>: To find and load an existing bean  

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<jsp:getProperty>: To retrieve the property of the specified bean and direct it as output. 

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Attribute used are id, class, scope, and beanName <jsp:useBean id=“bean1” class=“bean.class” />

Attributes used are name and property.

<jsp:setProperty>: To set the property of the specified bean 

Attributes used are name, property, value, and param

JSP Technology 

<jsp:forward>: To forward a request to a different page Attribute used is page  Example: <jsp:forward age=“other.jsp” /> 

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<jsp: param >: Used as a sub attribute with jsp:include and jsp:forward to pass additional request parameters Attributes used are name and value  Example <jsp:include page=“somepage.jsp”> <jsp:param name=“name1” value=“value1” /> <jsp:param name=“name2” value=“value2” /> 

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<jsp: include >: To insert a file into a particular JSP page 

Attributes used are page and flush

JSP Technology 

JSP comments  

In jsp comments can be included with <%--text--%> A comment cannot be inside another comment.

JSP Technology 

JSP Page Life Cycle  Translation 

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During the translation phase,the JSP engine reads a JSP page, parses it and validate the syntax of the tag used. In addition to checking the syntax, the engine perform other validity also 

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The attribute-value pairs in the directive and standard action are valid. The same Java Bean name is not used more than once in a translation phase. If we are using custom tag library, the library is valid The usage of custom tag is valid.

JSP Technology 

Compilation  In the compilation phase the java file generated in the previous step is compiled using the normal java compiler javac. All the java code that we write in declaration,Scriplets and expression is validated during this phase.  For example: the following declaration tag is a valid JSP tag and will pass to translation phase but it is not valid java declaration statement because it does not end with semicolon(;)

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Loading and instantiation  After successful compilation,the container load the servlet class into memory and instantiate it.

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Generated servlet class for a JSP page implements HttpJspPage interface extends the JspPage interface of same package which in turn extends the Servlet interface of the javax.servlet package. JspPage interface declares only two method jspInit() and jspDestroy() that must be implemented by all JSP page regardless of client-server protocol. HttpJspPage interface declares one method: _jspService()

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jspInit() 

The container calls the jspInit() to initialize the servlet instance. It is called before any other method, and is called only once for a servlet.

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_jspService() 

The container calls the _jspService() for each request, passing it the request and response objects. All of the HTML elements, JSP Scriplets and JSP expressions become a part of method during the translation phase.

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jspDestroy()  When the container decides to take instance of servlet it calls jspDestroy().  This is the last method which is called.  Note  We are not required to implement jspInit() and jspDestroy() method because they are automatically implemented.

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JSP implicit objects.  application: the application variable is of type javax.servlet.ServletContext. It refers to the environment of the web application to which the JSP page belongs. <%String path=application.getRealPath(“/webinf/counter.db”)%>  out: To write to the output stream out.println(“hello”)  page: To represent the current instance of the JSP page  request: To represent an object of HttpServletRequest used to retrieve the request data

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Response: To represent an object of HttpServletResponse used to write the HTML response output Session: To represent a session object