import javax.servlet.*;    
import javax.servlet.http.*;    
 
public class SessionCounter implements HttpSessionListener {
 private static int activeSessions = 0;
 public void sessionCreated(HttpSessionEvent se) { activeSessions++; }
 public void sessionDestroyed(HttpSessionEvent se) { 
 if(activeSessions > 0)  activeSessions--;    
 }
 public static int getActiveSessions() { return activeSessions; }    
}