[bbq]

I'm developing with an HttpSessionListener

My code is:

Code:

public class SessionListener implements HttpSessionListener, IHttpConstants {

  public void sessionCreated(HttpSessionEvent event) {
     HttpSession session = event.getSession();
    _log.info("Session [" + session.getId() + "] has been created.");
  }

  public void sessionDestroyed(HttpSessionEvent event) {
    HttpSession session = event.getSession();
    _log.info("Session [" + session.getId() + "] is about to be destroyed.");
    User user = (User) session.getAttribute(SESSION_ATTRIBUTE_USER);
    if (user != null) {
      _userTracker.logOut(user);
    }
  }

  private UserTracker _userTracker = UserTracker.getInstance();
  private static Category _log = Category.getInstance("log");
}

When the sessionDestroyed method is called a nexception appears : java.lang.IllegalStateException: getAttribute: Session already invalidated is thrown at the line where the user is retrieved from the session.

what is the problem?