package spp;

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 " +totalActiveSessions);
  }

  @Override
  public void sessionDestroyed(HttpSessionEvent arg0) 
  {
	totalActiveSessions--;
	System.out.println("sessionDestroyed - deduct one session from counter "+totalActiveSessions);
  }
}

  <listener>
     <listener-class>spp.SessionCounterListener</listener-class>
  </listener>

	protected void doGet(HttpServletRequest request, HttpServletResponse response) 
	   throws ServletException, IOException 
	{
		HttpSession session = request.getSession(); //sessionCreated()
		session.setAttribute("url", "spp");
		session.setMaxInactiveInterval(1*60);          //sessionDestroyed()
		//session.invalidate();                                  //sessionDestroyed()
		doExecute(request, response);
	}