Call a method just before a session expires

In this tutorial we gonna learn that how to call a specific method when a session is going to be destroyed or invalidated by the application container. First of all we need to know why we are doing this. Well it may have many applications but typically we use it for updating user counts, releasing resources etc. We could use HttpSessionListener and do the job in sessionDestroyed() method.

How to implement HttpSessionListener ?

To implement SessionListner we just have to make a class that implements HttpSessionListener and override the sessionDestroyed() method. If you want to call a method when a session is created then you can override sessionCreated() method. After overriding these methods you can do whatever you want to do. You can even get the data associated with that session in these methods.

Example :

package service;
import java.util.logging.Logger;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class SessionListner implements HttpSessionListener {
   
   static final Logger log = Logger.getAnonymousLogger();
   private static int totalActiveSessions;
  
   public static int getTotalActiveSession(){
  return totalActiveSessions;
   }
  
   @Override
   public void sessionCreated(HttpSessionEvent se) {
  totalActiveSessions++;
  
   }
  
   @Override
   public void sessionDestroyed(HttpSessionEvent se) {
  totalActiveSessions--;
                // se.getAttribute("username") if you want to get session data 
   }
}

Now after making this class you have to register this listener to your web.xml file. To do this just add below line of code.

<listener>
    <listener-class>service.SessionListner</listener-class>
</listener>

Now whenever any session will be invalidated or timed out, the sessionDestroyed method will be called.