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HttpSessionListener Example

By admin | December 17, 2011 | Updated : March 26, 2016 listener, servlet, 3 Comments
HttpSessionListener Example

HttpSessionListener Example explains about How to use HttpSessionListener in a web application

What is HttpSessionListener?

For knowing about HttpSessionListener, First we must understand session. Http protocol is a "stateless" protocol. The word stateless means Http protocol can't persist the information in between client and server. When a client sends a request for any resource, server receive the request and process the request and returns response.  After returning the response the server terminates the connection. When a client forwards a request for a particular resource, server consider each and every request as a separate request. In order to avoid this burden we use session. With the help of session tracking when a client request for any pages or resources container creates a session id for that particular request and return back the session id to the client along with the response object.

When I Use HttpSessionListener

Whenever a session created or destroyed, servlet container will invoke HttpSessionListener

javax.servlet.http.HttpSessionListener interface has following methods:

sessionCreated(HttpSessionEvent event)
  It will notify when the session is created.
sessionDestroyed(HttpSessionEvent event) 
  It will notify when the session gets invalidated.

Package Structure

HttpSessionListenerExample Example

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5">
    <listener>
        <listener-class>com.listener.HttpSessionListenerExample</listener-class>
    </listener>
</web-app>

HttpSessionListenerExample.java

package com.listener;

import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class HttpSessionListenerExample implements HttpSessionListener {

  private static int sessions;

  public static int getTotalActiveSession() {
    return sessions;
  }

  @Override
  public void sessionCreated(HttpSessionEvent arg) {
    sessions++;
    System.out.println("sessionCreated add one session into counter");
  }

  @Override
  public void sessionDestroyed(HttpSessionEvent arg) {
    sessions--;
    System.out.println("sessionDestroyed deduct one session from counter");
  }
}

Invoke HttpSessionListener From Servlet

HttpSession session = request.getSession(); //sessionCreated() method is invoked
session.setAttribute("url", "www.javatips.net"); 
session.invalidate();  //sessionDestroyed() method is invoked

Note

From Servlet API 3.0, we can use javax.servlet.annotation, so that web.xml is not necessary

Here we are using @WebListener annotation

HttpSessionListenerExample.java

package com.listener;

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

@WebListener
public class HttpSessionListenerExample implements HttpSessionListener {

  private static int sessions;

  public static int getTotalActiveSession() {
    return sessions;
  }

  @Override
  public void sessionCreated(HttpSessionEvent arg) {
    sessions++;
    System.out.println("sessionCreated add one session into counter");
  }

  @Override
  public void sessionDestroyed(HttpSessionEvent arg) {
    sessions--;
    System.out.println("sessionDestroyed deduct one session from counter");
  }
}

ListenerServletExample.java

package com.listener;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;


/**
* This servlet is used for showing an example about sessionListener
*/
@WebServlet("/ListenerServletExample")
public class ListenerServletExample extends HttpServlet {
    private static final long serialVersionUID = 1L;

   public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
      
       HttpSession session = request.getSession(); //sessionCreated() method is invoked
       session.setAttribute("url", "www.javatips.net");
       session.invalidate();  //sessionDestroyed() method is invoked
      
       PrintWriter out = response.getWriter();
       out.append("Session Created Successfully");
    }
}

Tomcat Console Output

sessionCreated add one session into counter
sessionDestroyed deduct one session from counter

 





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3 Responses to "HttpSessionListener Example"
  1. Sijo 2011-12-20 08:07:50.0 
    Hi admin,
I have tried this example, but sessionCreated(HttpSessionEvent event),sessionDestroyed(HttpSessionEvent event) methods not get executed
could you help me
  1. admin 2011-12-21 08:07:50.0 
    @Sijio,

Without any code, I cant able to check.
But my good assumption is that, you forget to register the listener in the web.xml. See the code below.

<listener-class>com.listener.HttpSessionListenerExample</listener-class>
  1. sijo 2011-12-22 08:07:50.0 
    Hi admin,

Now sessionCreated(HttpSessionEvent event), sessionDestroyed(HttpSessionEvent event) are invoked, I forgot to register the listner, thanks for pointing out the issue.

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