RabbitMQ——死信队列

RabbitMQ——死信队列

死信队列（Dead Letter Queue，DLQ）是 RabbitMQ 中的一种重要特性，用于处理无法被消费的消息，防止消息丢失。

死信的来源

在消息队列中，当消息满足一定条件而无法被正常消费时，这些消息会被发送到死信队列。满足条件的情况包括但不限于：

• 消息被拒绝（basic.reject 或 basic.nack）且不重新入队（requeue 参数为 false）。
• 消息过期（TTL，Time-To-Live）。
• 队列长度超过限制，无法再添加数据到mq中。

生产者

package com.weipch.rabbitmq.dlq;

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.GetResponse;
import com.weipch.util.RabbitMqUtils;

/**
 * @Author 方唐镜
 * @Create 2024-03-03 14:08
 * @Description
 */
public class Produce {


	private static final String NORMAL_EXCHANGE = "normal_exchange";


	public static void main(String[] args) throws Exception {
		Channel channel = RabbitMqUtils.getChannel();
        //模拟消息过期 10s
		//AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().expiration("10000").build();
		for (int i = 0; i < 10; i++) {
			String message = "hello world" + i;
			channel.basicPublish(NORMAL_EXCHANGE, "normal-routing-key", null, message.getBytes());
		}
	}
}

消费者

正常队列：

package com.weipch.rabbitmq.dlq;

import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.DeliverCallback;
import com.weipch.util.RabbitMqUtils;

import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Map;

/**
 * @Author 方唐镜
 * @Create 2024-03-03 13:50
 * @Description
 */
public class Consumer01 {


	private static final String NORMAL_EXCHANGE = "normal_exchange";
	private static final String DEAD_EXCHANGE = "dead_exchange";

	private static final String NORMAL_QUEUE = "normal_queue";
	private static final String DEAD_QUEUE = "dead_queue";


	public static void main(String[] args) throws Exception {
		Channel channel = RabbitMqUtils.getChannel();
		//声明死信交换机和队列
		channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
		channel.queueDeclare(DEAD_QUEUE, false, false, false, null);
		//绑定
		channel.queueBind(DEAD_QUEUE, DEAD_EXCHANGE, "dead-routing-key");


		//声明普通交换机和队列
		channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
		//在正常队列中设置死信参数 指定死信交换机和死信路由键
		Map<String, Object> map = new HashMap<>();
		map.put("x-dead-letter-exchange", DEAD_EXCHANGE);
		map.put("x-dead-letter-routing-key", "dead-routing-key");
		//最大长度
		//map.put("x-max-length", 6);
		channel.queueDeclare(NORMAL_QUEUE, false, false, false, map);
		channel.queueBind(NORMAL_QUEUE, NORMAL_EXCHANGE, "normal-routing-key");
		DeliverCallback deliverCallback = (consumerTag, delivery) -> {
			String message = new String(delivery.getBody(), StandardCharsets.UTF_8);
			if (message.contains("5")){
				System.out.println("Consumer01接收消息：" + message + "，此消息被拒绝");
				//拒绝消息并把消息丢入死信队列
				channel.basicReject(delivery.getEnvelope().getDeliveryTag(), false);
			}else {
				System.out.println("Consumer01接收消息：" + message);
				channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
			}
		};
		channel.basicConsume(NORMAL_QUEUE, false, deliverCallback, (consumerTag, e) -> {});
	}
}

死信队列：

package com.weipch.rabbitmq.dlq;

import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
import com.weipch.util.RabbitMqUtils;

import java.nio.charset.StandardCharsets;
import java.util.HashMap;
import java.util.Map;

/**
 * @Author 方唐镜
 * @Create 2024-03-03 13:50
 * @Description
 */
public class Consumer02 {
	
	private static final String DEAD_QUEUE = "dead_queue";

	public static void main(String[] args) throws Exception {
		Channel channel = RabbitMqUtils.getChannel();
		channel.basicConsume(DEAD_QUEUE, true,
			(consumerTag, delivery) -> System.out.println("Consumer02:" + new String(delivery.getBody(), StandardCharsets.UTF_8)),
			(consumerTag, e) -> {});
	}
}

生产者发送消息到正常队列，而消费者负责消费正常队列的消息。当消息被消费者拒绝并不再重新投递时，消息会被发送到死信队列。