code: public void addConfigurationListener(NodeConfigListener listener) {
          StanzaListener conListener = new NodeConfigTranslator(listener);
          configEventToListenerMap.put(listener, conListener);
          pubSubManager.getConnection().addSyncStanzaListener(conListener, new EventContentFilter(EventElementType.configuration.toString()));
      }
docs: Register a listener for configuration events.  This listener
  will get called whenever the node's configuration changes.
  
  @param listener The handler for the event