Return Listener用于处理一些不可路由的消息！

正常情况：我们的消息生产者，通过指定一个Exchange和RoutingKey，把消息送达到某一个队列中去，然后我们的消费者监听队列，进行消费处理操作！

异常情况：在某些情况下，如果我们在发送消息的时候，当前的Exchange不存在或者指定的路由key路由不到，这个时候如果我们需要监听这种不可达的消息，就需要使用Return Listener！

在基础API中有一个关键的配置项

Mandatory：如果为true，则监听器会接收到路由不可达的消息，然后进行后续处理，如果为false，那么Broker端自动删除该消息！

消费端代码

package com.javaxl.rabbitmqapi.returnlistener;

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.QueueingConsumer;

/**
 * @author 小李飞刀
 * @site www.javaxl.com
 * @company
 * @create  2019-11-20 9:58
 */
public class Consumer {
    public static void main(String[] args) throws Exception {
        ConnectionFactory connectionFactory = new ConnectionFactory();
        connectionFactory.setHost("192.168.147.146");
        connectionFactory.setPort(5672);
        connectionFactory.setVirtualHost("/");

        Connection connection = connectionFactory.newConnection();
        Channel channel = connection.createChannel();

        String exchangeName = "test_return_exchange";
        String routingKey = "return.#";
        String queueName = "test_return_queue";

        channel.exchangeDeclare(exchangeName, "topic", true, false, null);
        channel.queueDeclare(queueName, true, false, false, null);
        channel.queueBind(queueName, exchangeName, routingKey);

        QueueingConsumer queueingConsumer = new QueueingConsumer(channel);

        channel.basicConsume(queueName, true, queueingConsumer);

        while(true){
            QueueingConsumer.Delivery delivery = queueingConsumer.nextDelivery();
            String msg = new String(delivery.getBody());
            System.err.println("消费者: " + msg);
        }

    }
}

生产端代码

package com.javaxl.rabbitmqapi.returnlistener;

import com.rabbitmq.client.*;

import java.io.IOException;

/**
 * @author 小李飞刀
 * @site www.javaxl.com
 * @company
 * @create  2019-11-20 9:44
 */
public class Producer {
    public static void main(String[] args) throws Exception {
        ConnectionFactory connectionFactory = new ConnectionFactory();
        connectionFactory.setHost("192.168.147.146");
        connectionFactory.setPort(5672);
        connectionFactory.setVirtualHost("/");

        Connection connection = connectionFactory.newConnection();
        Channel channel = connection.createChannel();

        String exchange = "test_return_exchange";
        String routingKey = "return.save";
        String routingKeyError = "abc.save";

        String msg = "Hello RabbitMQ Return Message";


        channel.addReturnListener(new ReturnListener() {
            @Override
            public void handleReturn(int replyCode, String replyText, String exchange,
                                     String routingKey, AMQP.BasicProperties properties, byte[] body) throws IOException {

                System.err.println("---------handle  return----------");
                System.err.println("replyCode: " + replyCode);
                System.err.println("replyText: " + replyText);
                System.err.println("exchange: " + exchange);
                System.err.println("routingKey: " + routingKey);
                System.err.println("properties: " + properties);
                System.err.println("body: " + new String(body));
            }
        });

        //消息投递成功，会被消费者所消费
//        channel.basicPublish(exchange, routingKey, true, null, msg.getBytes());
        //消息不可达，将触发ReturnListener
         channel.basicPublish(exchange, routingKeyError, true, null, msg.getBytes());
    }
}

over.......