第三章 （12-14）死信队列

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到另一个Exchange，这个Exchange就是DLX

消息变成死信队列的几种情况

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

死信队列描述

• DLX也是一个正常的Exchange，和一般的额Exchange没有区别，它能在任何的队列上被制定，实际上就是设置某个队列的属性
• 当这个队列中有死信时，RabbitMQ就会自动将这个消息重新发布到设置的Exchange上去，进而被路由到另一个队列
• 可以监听这个队列消息做相应的处理，这个特性可以弥补RabbitMQ3.0以前支持的immediate参数功能

死信队列设置

• 首先需要设置死信队列的exchange和queue，然后进行绑定
  • Exchange：dlx.exchange
  • Queue：dlx.queue
  • RoutingKey: #
• 然后我们进行正常声明交换机、队列、绑定，只不过我们需要在队列上加一个参数即可：arguments.put("x-dead-letter-exchange", "dlx.exchange");
• 这样消息在过期、requeue、队列在达到最大长度时，消息就可以直接路由到死信队列！

代码实现

生产端

package club.yunqiang.rabbitmqapi.dlx;

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

import java.io.IOException;
import java.util.concurrent.TimeoutException;

/**
 * @author 张云强
 * @date 2019/12/7
 */
public class Producer {

    public static void main(String[] args) throws IOException, TimeoutException {
        ConnectionFactory connectionFactory = new ConnectionFactory();
        connectionFactory.setPort(5672);
        connectionFactory.setVirtualHost("/");
        connectionFactory.setHost("localhost");

        Connection connection = connectionFactory.newConnection();

        Channel channel = connection.createChannel();

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

        String msg = "Hello Rabbit MQ DLX Message";
        for (int i = 0; i < 1; i++) {
            AMQP.BasicProperties properties = new AMQP.BasicProperties().builder()
                    .deliveryMode(2)
                    .contentEncoding("UTF-8")
                    .expiration("10000")
                    .build();
            channel.basicPublish(exchange, routingKey, true, properties, msg.getBytes());
        }
    }

}

消费端

package club.yunqiang.rabbitmqapi.dlx;

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

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeoutException;

/**
 * @author 张云强
 * @date 2019/12/7
 */
public class Consumer {

    public static void main(String[] args) throws IOException, TimeoutException {
        ConnectionFactory connectionFactory = new ConnectionFactory();
        connectionFactory.setPort(5672);
        connectionFactory.setVirtualHost("/");
        connectionFactory.setHost("localhost");

        Connection connection = connectionFactory.newConnection();

        Channel channel = connection.createChannel();

        // 声明一个普通队列
        String exchangeName = "test_dlx_exchange";
        String routingKey = "dlx.#";
        String queueName = "test_dlx_queue";
        Map<String, Object> arguments = new HashMap<>();
        arguments.put("x-dead-letter-exchange", "dlx.exchange");
        // 通过arguments参数给队列指定死信队列
        channel.queueDeclare(queueName, true, false, false, arguments);
        channel.exchangeDeclare(exchangeName, "topic", true, false, null);
        channel.queueBind(queueName, exchangeName, routingKey);

        // 死信队列声明
        channel.exchangeDeclare("dlx.exchange", "topic", true, false, null);
        channel.queueDeclare("dlx.queue", true, false, false, null);
        channel.queueBind("dlx.queue", "dlx.exchange", "#");

        // 接收消息
        channel.basicConsume(queueName, true, new MyConsumer(channel));
    }
}

消费者

package club.yunqiang.rabbitmqapi.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;

/**
 * @author 张云强
 * @date 2019/12/7
 */
public class MyConsumer extends DefaultConsumer {


    /**
     * Constructs a new instance and records its association to the passed-in channel.
     *
     * @param channel the channel to which this consumer is attached
     */
    public MyConsumer(Channel channel) {
        super(channel);
    }

    @Override
    public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
        System.out.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));
    }
}

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