Java Servlets (more)

Java Servlets CS-422

Application Mapping •

Your servlet application will be mapped to a directory structure: – “myapp” maps to some directory C:/docs/apps/myapp – in the myapp directory create a directory called “Web-inf” • in Web-inf create – – – –

classes jsp lib - use this for common things like JDBC drivers sessions

• these directories are used for the various components of your application

– when invoking your servlet • http://www.myserver.com/myapp/servlet/servletname • the “magic name” myapp/setvlet will really refer to – c:docs/apps/myapp/Web-inf/classes

Deploying your application •

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To deploy a servlet based application create a .war (web archive) file containing all of the files needed for the application and place it on the server the servlet container will work from the web archive extracting files as needed – the base JVM has all of the classes it needed for working with files in the various versions of zipped files.

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Use the JDK JAR utility to create your .war file – ex cd myapp; jar -cvf myapp.war (make sure that …JDKnnn/bin is in your path and all of the files in the current directory will be placed into the file myapp.war – copy the .war file to the webapp directory of your server and its work – make sure to back-up both your development directory and your deployed war file.

Servlet Life •

A servlet can come into existence for two reasons: – it was configured to be loaded on start-up of the servlet engine – a user request called for it

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a servlet object is created on the main thread init( ) is started on a secondary thread – the servlets init( ) method is guaranteed to be called once (and only once) for the life of a given servlet. – init( ) is guaranteed to complete before any service methods are invoked.

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the main thread for the servlet will terminate at the end of the init( ) when a request for the servlet is received the servlet engine spawns a new thread and calls the appropriate service( ) method – in the case of http this will be: • • • • • •

doGet doPost doDelete doOptions doPut doTrace

Servlet Life (more) •

Once the servlets life cycle us up (when all associated threads quiesce) the destroy( ) method will automatically be run

Servlet APIs •

The servlet APIs are split into two packages: – javax.servlet • contains classes and interfaces that implement generic, protocol independent servlets, having this generiv layer allows it to be extended other protocols (like IIOP)

– javax.servlet.http • extends javax.servlet for the HTTP protocol

– javax implies it is an official java extension • TOMCAT is the official reference implementation

Scope Page

N/A

Request

request.setAttribute(key) request.getAttribute(key)

Session

session.setAttribute(key) session.getAttribute(key

Application

getServletContext() SetAttribute(key,obj) GetServletContext() GetAttribute(key)

Available to the handling servlet only(within its service method). These are usually method instance variables Available to the handling servlet or any servlet or JSP that control is forwarded to Available to any servlet or JSP within the same scope. Most common example of a session scoped object would be a shopping cart. Available to any servlet or JSP within the same webapp. Usually obtained in the init( ) method. Note that ServletContext object hold objects of application scope. An typical application scoped object

J2EE Application Servers • • • • • •

Tomcat – Apache Foundation – Open Source JRUN – Macromedia WebSphere – IBM BEA Weblogic – BEA Sun Java System Application Server – SUN Oracle Application Server – Oracle Corp.

Deployment • Tomcat v.4 (Apache Foundation, Jakarta Project) – Implements the Servlet 2.3 and JSP 1.2 Specifications

• Servlet 2.3 Specification – Outlines requirements for deploying servlets • Directory Structure • Deployment Descriptors

Directory Structure • /application • /application/WEB-INF – Web.xml (deployment Descriptor)

• /application/WEB-INF/classes – Compiled class files – May be a WAR (Web Archive file containing all class files); create using the JAR application found in the JSDK bin directory

Deployment Descriptors • XML file describing the application – Used by the server to deploy the application – DTD is at java.sun.con/j2ee/dtds/web-app_2_2.dtd

Web.xml (sample) <web-app> CS422Sample <description>Steflik’s Sample App for CS422 <servlet> <servlet-name>BrowserDataServlet <servlet-class>BrowserDataServlet <servlet-mapping> <servlet-name>BrowserDataServlet /steflik/BrowserDataServlet <servlet-mapping>

Web Application Archive files • jar cvf mywebapp.war