code: @Handler
      public void onOutput(Output<?> event, WebAppMsgChannel appChannel)
              throws InterruptedException {
          appChannel.handleAppOutput(event);
      }
docs: Handles output from the application. This may be the payload
  of e.g. a POST or data to be transferes on a websocket connection.
  
  @param event the event
  @param appChannel the application layer channel
  @throws InterruptedException the interrupted exception