2.7 RabbitMQ高级特效-死信队列

DLX ,Dead-Letter-Exchange利用DLX，当消息在一个队列中变成死信（dead message）之后，它能被重新publish到另外一个Exchange，这个Exchange就是DLX。
消息变成死信有以下几种情况:

    1.消息被拒绝（basic.reject/basic.nack）并且requeue=false
    2.消息TTL过期。。
    3.队列达到最大长度。

DLX也是一个正常的Exchange，和一般的Exchange没有区别，它能在任何的队列上被指定，实际上就是设置某个队列的属性。当这个队列中有死信的时，RabbitMQ就会自动的将这个消息重新发布到设置的Exchange上去，进二被路由到另外一个队列。
可以监听这个队列中消息做相应的处理，这个特性可以弥补RabbitMQ3.0以前支持的immediate参数的功能。
死信队列的设置：

   1 首先需要设置死信队列的Exchange和queue，然后绑定：
        Exchange：dlx.exchange
        Queue：dlx.queue
        RoutingKey：#
    2 然后进行正常声明交换机、队列、绑定，只不过我们需要在对别加上一个参数即可：arguments.put("x-dead-letter-exchange","dlx.exchange")。这样消息在过期、qequeue、队列达到最大长度时，消息就可以直接路由到死信队列！

消费者端代码

package com.star.movie.dlx;

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DefaultConsumer;
import com.rabbitmq.client.Envelope;

import java.io.IOException;

/**
 * @Description：
 * @author:kaili
 * @Date: 2019-04-22 20:10
 **/
public class MyDlxConsumer extends DefaultConsumer {

    private Channel channel;

    public MyDlxConsumer(Channel channel) {
        super(channel);
        this.channel = channel;
    }

    @Override
    public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
        System.err.println("----------- consume message ----------");
        System.err.println("consumerTag: " + consumerTag);
        System.err.println("envelope: " + envelope);
        System.err.println("properties: " + properties);
        System.err.println("body: " + new String(body));
    }
}

package com.star.movie.dlx;

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.star.movie.common.Constant;

import java.util.HashMap;
import java.util.Map;

/**
 * @Description：
 * @author:kaili
 * @Date: 2019-04-22 20:08
 **/
public class DlxConsumer {
    public static void main(String[] args) throws Exception{
        Connection connection = Constant.getConnection();
        Channel channel = connection.createChannel();


        // 这就是一个普通的交换机 和 队列 以及路由
        String exchangeName = "test_dlx_exchange";
        String routingKey = "dlx.#";
        String queueName = "test_dlx_queue";

        channel.exchangeDeclare(exchangeName, "topic", true, false, null);

        Map<String, Object> agruments = new HashMap<String, Object>();
        agruments.put("x-dead-letter-exchange", "dlx.exchange");
        //这个agruments属性，要设置到声明队列上
        channel.queueDeclare(queueName, true, false, false, agruments);
        channel.queueBind(queueName, exchangeName, routingKey);

        //要进行死信队列的声明:
        channel.exchangeDeclare("dlx.exchange", "topic", true, false, null);
        channel.queueDeclare("dlx.queue", true, false, false, null);
        channel.queueBind("dlx.queue", "dlx.exchange", "#");

        channel.basicConsume(queueName, true, new MyDlxConsumer(channel));
    }
}

生产者端代码

package com.star.movie.dlx;

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.star.movie.common.Constant;

/**
 * @Description：
 * @author:kaili
 * @Date: 2019-04-22 20:07
 **/
public class DlxProducer {

    public static void main(String[] args) throws Exception{
        Connection connection = Constant.getConnection();
        Channel channel = connection.createChannel();

        String exchange = "test_dlx_exchange";
        String routingKey = "dlx.save";

        String msg = "Hello RabbitMQ DLX Message";

        for(int i =0; i<1; i ++){
            //设置消息有效期
            AMQP.BasicProperties properties = new AMQP.BasicProperties.Builder()
                    .deliveryMode(2)
                    .contentEncoding("UTF-8")
                    .expiration("10000")
                    .build();
            channel.basicPublish(exchange, routingKey, true, properties, msg.getBytes());
        }
    }
}