• When your web application is running in the web container, the following tasks will be done by the web container and developer.
1. Creating ServletContext object
2. Destroying ServletContext object
3. Creating HttpServletRequest object
4. Destroying HttpServletRequest object
5. Creating HttpSession object
6. Destroying HttpSession object
7. Adding attributes to ServletContext.
8. Removing Attributes from ServletContext
9. Replacing attributes from ServletContext
10. Adding attributes to HttpServletRequest
11. Removing Attributes from HttpServletRequest
12. Replacing attributes from HttpServletRequest
13. Adding attributes to HttpSession
14. Removing Attributes from HttpSession
15. Replacing attributes from HttpSession
16. Passivating HttpSession object
17. Activating HttpSession object
• Following is the list of Listener interfaces available in Servlet via the Servlet API.
| Listerner Interface | Event Class | Task will be listened |
|---|---|---|
| ServletContextListener | ServletContextEvent | Task 1, Task 2 |
| ServletRequestListener | ServletRequestEvent | Task 3,Task 4 |
| HttpSessionListener | HttpSessionEvent | Task 5, Task 6 |
| ServletContextAttributeListener | ServletContextAttributeEvent | Task 7, Task 8, Task 9 |
| ServletRequestAttributeListener | ServletRequestAttributeEvent | Task 10, Task 11,Task 12 |
| HttpSessionAttributeListener | HttpSessionBindingEvent | Task 13,Task 14,Task15 |
| HttpSessionBindingListener | HttpSessionBIndingEvent | |
| HttpSessionActivationListener | HttpSessionEvent | Task 16,Task 17 |
• Write your own listener class by implementing the required Listener interface.
• Override the responding methods of the listener interface that you are implementing.
Class MyListner implements ServletContextListener{
Public void contextInitialized(sce){
//your code here
}
Public void contextDestroyed(sce){
//your code here
Ctx=sce.getServletContext();
}
}
• Register the listener by writing the following in web.xml:
<listener> <listener-class>com.jtc.MyListener</listener-class> </listener>
• Write your own listener class by implementing the required Listener interface.
• Override the corresponding methods of the Listener interface that you are implementing.
• Register the listing by using @WebListener annonation.
@webListerner
Class MyListner implements ServletContextListener{
Public void contextInitialized(sce){
//your code here
}
Public void contextDestroyed(sce){
//your code here
Ctx=sce.getServletContext();
}
}
Note: All the listeners configured will be initialised by the container at container start-up.
• Creates the ServletContext object.
o ServletContext sctx=new ServlletContextImpl();
• Gets the context parameters from web.xml and stores them in a ServletContext object.
• Creates a ServletContextEvent
o ServletContextEventListener sce=new ServletContextEvent(sctx);
• Create the ServletContextListener object.
o ServletContextListener listner = new ServletContextListenerImple();
• Invoke the contextinitialized() method with the ServletContextListerner object.
o Listener.contextInitialized(sce).
• Invoke the contextDestroyed() method with ServletContextListener object
o Listener.contextDestoryed(sce).
• Destroys the ServletContext object.
File Required For Program
1. Index.html
2. TestServlet.java
3. MyContextListener.java
4. MyContextAttributeListerner.java
5. MySessionListener.java
6. MyRequestListener.java
7. Web.xml
1. Index.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type"
content="text/html; charset=ISO-8859-
1">
<title>Insert title here</title>
</head>
<body>
<h1>JTC</h1>
<h2>Listener Example</h2>
<form action="test.jtc" method="post">
Enter Email:<input type="text"
name="email">
<br/>
<input type="submit" value="submit">
</form>
</body>
</html>
2. TestServlet.java
package com.jtcindia.Servlet;
import java.io.IOException;
import java.io.Writer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
/*
* @Author : Som Prakash Rai
* @Join : JTC
* @visit : www.jtcindia.org
*@Call :+91-9990399111
* */
public class TestServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
System.out.println("TestServlet-> service()");
System.out.println("Acccessing Session object");
HttpSession session = req.getSession();
String eml = req.getParameter("email");
ServletContext ctx = getServletContext();
System.out.println("Storing attribute in Context");
ctx.setAttribute("email", eml);
System.out.println("Replacing attributes in Context");
ctx.setAttribute("email", "som@jtc.com");
System.out.println("Removing attribute in Context");
ctx.removeAttribute("email");
System.out.println("validating Session Objects");
session.invalidate();
Writer out = res.getWriter();
out.write("<h1>Verify the server console");
}
}
3. MyContextListener.java
package com.jtcindia.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
/*
* @Author : Som Prakash Rai
* @Join : JTC
* @visit : www.jtcindia.org
*@Call :+91-9990399111
* */
public class MyContextListener implements
ServletContextListener {
public MyContextListener() {
System.out.println("** MyContextListener() def
consol ");
}
@Override
public void contextDestroyed(ServletContextEvent event) {
ServletContext
ctx = event.getServletContext();
System.out.println("ContextDestroyed:" + ctx);
}
@Override
public void contextInitialized(ServletContextEvent event) {
ServletContext
ctx = event.getServletContext();
System.out.println("ContextInitialized:" + ctx);
}
}
4. MyContextAttributeListener.java
package com.jtcindia.Servlet;
import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
/*
* @Author : Som Prakash Rai
* @Join : JTC
* @visit : www.jtcindia.org
*@Call :+91-9990399111
* */
public class MyContextAttributListener implements
ServletContextAttributeListener {
public MyContextAttributListener() {
System.out.println("** MyContextAttributListener()
Def Console ");
}
@Override
public void
attributeAdded(ServletContextAttributeEvent event) {
String nm = event.getName();
String val = event.getValue().toString();
System.out.println("**
AttributeAdded(): "+nm+"\
t "+val);
}
@Override
public void
attributeRemoved(ServletContextAttributeEvent event) {
String nm = event.getName();
String val = event.getValue().toString();
System.out.println("attributeRemove():" + n m + "\t" + val)
}
@Override
public void
attributeReplaced(ServletContextAttributeEvent event) {
String nm = event.getName();
String val = event.getValue().toString();
System.out.println("attributeRemove():" + n m + "\t" + val);
}
}
5. MySessionListener.java
package com.jtcindia.Servlet;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
/*
* @Author : Som Prakash Rai
* @Join : JTC
* @visit : www.jtcindia.org
*@Call :+91-9990399111
* */
public class MySessionListener implements
HttpSessionListener {
public MySessionListener() {
System.out.println("**
MySessionListener() def Cons ");
}
@Override
public void sessionCreated(HttpSessionEvent arg0) {
System.out.println("SessionCreated");
}
@Override
public void sessionDestroyed(HttpSessionEvent arg0) {
System.out.println("**SessionDestroyed");
}
}
6. MyRequestListener.java
package com.jtcindia.Servlet;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
/*
* @Author : Som Prakash Rai
* @Join : Java Training Center
* @visit : www.jtcindia.org
*@Call :+91-9990399111
* */
public class MyRequestListener implements
ServletRequestListener {
public MyRequestListener() {
System.out.println("MyRequestListener()
def console ");
}
@Override
public void
requestDestroyed(ServletRequestEvent arg0) {
System.out.println("requestDestroyed");
}
@Override
public void
requestInitialized(ServletRequestEvent arg0) {
System.out.println("requestInitialized");
}
}
7. Web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-appxmlns:xsi="http://www.w3.org/2001/XMLSchemainstance" xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
id="WebApp_ID" version="3.0">
<display-name>Jtc27</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>testServlet</servlet-name>
<servletclass>com.jtcindia.Servlet.TestServlet</servletclass>
</servlet>
<servlet-mapping>
<servlet-name>testServlet</servlet-name>
<url-pattern>/test.jtc</url-pattern>
</servlet-mapping>
<listener>
<listenerclass>com.jtcindia.Servlet.MyContextListener</listener-class>
</listener>
<listener>
<listenerclass>com.jtcindia.Servlet.MyContextAttributListener
</listener-class>
</listener>
<listener>
<listenerclass>com.jtcindia.Servlet.MyRequestListener</listener-class>
</listener>
<listener>
<listenerclass>com.jtcindia.Servlet.MySessionListener</listener-class>
</listener>
</web-app>