18-RabbitMQ高级特性-死信队列

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
DLX也是一个正常的Exchange, 和一般的Exchange没有区别, 他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时,RabbitMQ就会自动的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
可以监听这个队列的消息做相应的处理, 这个特征可以弥补RabbitMQ3.0以前支持的immediate参数功能

消息变成死信的情况

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

死信队列的设置

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: #

然后进行正常的声明交换机, 队列, 绑定, 只不过需要在队列上添加一个参数即可

arguments.put("x-dead-letter-exchange","dlx.exchange");

这样消息在过期, requeue=false, 队列在达到最大长度时, 消息就直接路由到死信队列了!

死信队列代码实现

消费者

package com.dance.redis.mq.rabbit.dlx;

import com.dance.redis.mq.rabbit.RabbitMQHelper;
import com.rabbitmq.client.*;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.TimeUnit;
 
public class Receiver4DLXtExchange {
 
    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMQHelper.getChannel();
        // 声明正常的 exchange queue 路由规则
        String queueName = "test_dlx_queue";
        String exchangeName = "test_dlx_exchange";
        String routingKey = "group.*";
        RabbitMQHelper.exchangeDeclare(channel,exchangeName,RabbitMQHelper.EXCHANGE_TYPE_TOPIC);

        //    注意在这里要加一个特殊的属性arguments: x-dead-letter-exchange
        Map<String, Object> arguments = new HashMap<>();
        // 指定死信队列
        arguments.put("x-dead-letter-exchange", "dlx.exchange");
        // 指定死信队列的路由规则
        arguments.put("x-dead-letter-routing-key", "dlx.*");
        RabbitMQHelper.queueDeclare(channel,queueName,true,arguments);
        channel.queueBind(queueName, exchangeName, routingKey);

        // 声明死信队列
        // dlx declare:
        RabbitMQHelper.exchangeDeclare(channel,"dlx.exchange",RabbitMQHelper.EXCHANGE_TYPE_TOPIC);
        channel.queueDeclare("dlx.queue", false, false, false, null);
        channel.queueBind("dlx.queue", "dlx.exchange", "#");
        Consumer consumer = new DefaultConsumer(channel) {
            @Override
            public void handleDelivery(String consumerTag,
                                       Envelope envelope,
                                       AMQP.BasicProperties properties,
                                       byte[] body)
                    throws IOException {
                // 拒绝并且不重回队列, 这样就会进入死信队列
                channel.basicReject(envelope.getDeliveryTag(),false);
            }
        };
        //    参数：队列名称、是否自动ACK、Consumer
        channel.basicConsume(queueName, false, consumer);
        //等待回调函数执行完毕之后，关闭资源。
        TimeUnit.SECONDS.sleep(50);
        channel.close();
        RabbitMQHelper.closeConnection();
    }
}

生产者

package com.dance.redis.mq.rabbit.dlx;

import com.dance.redis.mq.rabbit.RabbitMQHelper;
import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;

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

public class Sender4DLXExchange {


    public static void main(String[] args) throws Exception {
        Channel channel = RabbitMQHelper.getChannel();
        String exchangeName = "test_dlx_exchange";
        String routingKey = "group.dlx";
        Map<String, Object> headers = new HashMap<>();
        AMQP.BasicProperties props = new AMQP.BasicProperties.Builder()
                .deliveryMode(2)
                .contentEncoding("UTF-8")
                .headers(headers).build();
        String msg = "Hello World RabbitMQ 4 DLX Exchange Message ... ";
        channel.basicPublish(exchangeName, routingKey, props, msg.getBytes());
    }

}