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) -> {});}
}