A Simple HttpSessionListener Example – Active Sessions Counter

Posted on December 5, 2009

By mkyong

Here’s a simple “HttpSessionListener” example to keep track the total number of active sessions in a web application. If you want to keep monitor your session’s create and remove behavior, then consider this listener.

Java Source

package com.mkyong;
 
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
 
public class SessionCounterListener implements HttpSessionListener {
 
  private static int totalActiveSessions;
 
  public static int getTotalActiveSession(){
 return totalActiveSessions;
  }
 
  @Override
  public void sessionCreated(HttpSessionEvent arg0) {
 totalActiveSessions++;
 System.out.println("sessionCreated - add one session into counter");
  }
 
  @Override
  public void sessionDestroyed(HttpSessionEvent arg0) {
 totalActiveSessions--;
 System.out.println("sessionDestroyed - deduct one session from counter");
  } 
}

web.xml

 ...>
        
  com.mkyong.SessionCounterListener

How it work?

- If a new session is created , e.g “request.getSession();” , the listener’s sessionCreated() will be executed.
- If a session is destroyed, e.g session’s timeout or “session.invalidate()”, the listener’s sessionDestroyed() will be executed.

  HttpSession session = request.getSession(); //sessionCreated() is executed
  session.setAttribute("url", "mkyong.com"); 
  session.invalidate();  //sessionDestroyed() is executed