Understanding Session Lifecycle Events

HttpSessionEvent class gives notifications for changes to sessions within a web application. HttpSessionListener receives notifications of changes to the list of active sessions in a web application and perform some action. HttpSessionListener is used to perform some important tasks when a session is created or destroyed. For example: counting the number of active session.

Methods of HttpSessionListener

Example of HttpSessionListener

In this example we will create a session listener that will count the number of active sessions in a web application.

MySessionCounter.java

import javax.servlet.http.*;

public class MySessionCounter implements HttpSessionListener {

    private static int sessionCount; 
    
    public int getActiveSession()
    {
        return sessionCount;
    }
   
    public void sessionCreated(HttpSessionEvent e) 
    {   
        sessionCount++;  
    }

    public void sessionDestroyed(HttpSessionEvent e) 
    {
        sessionCount--;
    }
}

web.xml

<web-app ...>
    <listener>
        <listener-class>MySessionCounter</listener-class>
    </listener>
</web-app>