code: public void startReturnHandlerProcessor() {
  
          final SendQueue<Response<Object>> webResponseSendQueue = webResponseQueue.sendQueue();
  
          responseQueue.startListener(new ReceiveQueueListener<Response<Object>>() {
  
              @Override
              public void receive(Response<Object> response) {
  
  
                  final Request<Object> originatingRequest = response.request().originatingRequest();
  
                  if (originatingRequest == null) {
                      callbackManager.handleResponse(response);
                  } else if (originatingRequest instanceof HttpRequest || originatingRequest instanceof WebSocketMessage) {
                      webResponseSendQueue.send(response);
                  } else {
                      callbackManager.handleResponse(response);
                  }
              }
  
              @Override
              public void empty() {
                  webResponseSendQueue.flushSends();
  
              }
  
              @Override
              public void limit() {
                  webResponseSendQueue.flushSends();
  
              }
  
              @Override
              public void shutdown() {
  
              }
  
              @Override
              public void idle() {
                  webResponseSendQueue.flushSends();
  
              }
  
              @Override
              public void startBatch() {
  
              }
          });
      }
docs: Handles responses coming back from services.