静默地将作业返回队列

Question

I have a RabbitMQ with a job queue defined, and I'm consuming it with the Java through Spring Framework. I know that, if I throw an exception somewhere in the code while processing the job which I received from the queue, will return the job to the queue. But, is there some other way to return a job to the queue, without throwing and exception, or returning a job "manually" to the queue?

Answer 1

The solution may depend on abstraction that you use:

• Spring Cloud Streams uses Spring AMPQ
• Spring AMQP uses RabbitMQ Java Client
• RabbitMQ Java Client

---

Spring Cloud Streams

I would do this using a Spring Cloud Stream Processor that processes messages and sets the routingKeyExpression .

The bindings:

=> theSourceQueue 
   => myProcessor(message) consumes messages and setts routing key as a header
      => DestinationExchange 
         => route 1 => theSourceQueue
         => route 2 => ?

---

Spring AMQP

import com.rabbitmq.client.Channel;
import org.springframework.amqp.support.AmqpHeaders;
import org.springframework.messaging.handler.annotation.Header;
import org.springframework.stereotype.Component;

import java.io.IOException;

@Component
public class Receiver {
    @RabbitListener(queues = "my-messages")
    public void receiveMessage(String payload, Channel channel, @Header(AmqpHeaders.DELIVERY_TAG) long deliveryTag) throws IOException {
        System.out.println("Received message: `" + payload + "`, deliveryTag: " + deliveryTag);
        channel.basicNack(deliveryTag, false, true);
    }
}

---

RabbitMQ Java Client

You can go to the lower layer too and use negative acknowledgement and re-queue :

This example rejects two messages with a single call to the broker (the second argument on basicNack is the multiple flag):

 GetResponse gr1 = channel.basicGet("some.queue", false); GetResponse gr2 = channel.basicGet("some.queue", false); channel.basicNack(gr2.getEnvelope().getDeliveryTag(), true, true); 

When a message is requeued, it will be placed to its original position in its queue, if possible. If not (due to concurrent deliveries and acknowledgements from other consumers when multiple consumers share a queue), the message will be requeued to a position closer to queue head.