code: public final void addWebSocketPushListener(final String sessionId,
              final WebSocketPushListener wsListener) {
  
          sessionIdWsListeners.put(sessionId, wsListener);
          wsListeners.push(wsListener);
  
          this.wsListener = wsListener;
  
          if (pushQueueOnNewWebSocketListener) {
              pushWffBMBytesQueue();
          }
  
      }
docs: adds the WebSocket listener for the given WebSocket session
  
  @param sessionId
  the unique id of WebSocket session
  @param wsListener
  @since 2.1.0
  @author WFF