code: @Override
  	public void addEventListener(final EventListener listener) {
  		super.addEventListener(listener);
  		if ((listener instanceof HttpSessionActivationListener)
  				|| (listener instanceof HttpSessionAttributeListener)
  				|| (listener instanceof HttpSessionBindingListener)
  				|| (listener instanceof HttpSessionListener)) {
  			if (_sessionHandler != null) {
  				_sessionHandler.addEventListener(listener);
  			}
  		}
  
  	}
docs: If the listener is a servlet context listener and the context is already
  started, notify the servlet context listener about the fact that context
  is started. This has to be done separately as the listener could be added
  after the context is already started, case when servlet context listeners
  are not notified anymore.
  
  @param listener to be notified.