public void addListener(ResourceNotificationListener listener){
  if (listener == null) {
    logger.error("Attempting to add null listener");
  }
  listeners.add(listener);
}

public void addListener ( ResourceNotificationListener listener ) { if ( listener == null ) { logger . error ( "Attempting to add null listener" ) ; } listeners . add ( listener ) ; }
add a listener that will be informed in the event of a resource notification .
