RabbitMQ 死信队列是什么鬼？

Exchange: dlx.exchange
Queue: dlx.queue
RoutingKey: # 代表接收所有路由 key

import com.rabbitmq.client.AMQP;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
public class DlxProducer {
    public static void main(String[] args) throws Exception {
    //设置连接以及创建 channel 湖绿
        String exchangeName = "test_dlx_exchange";
        String routingKey = "item.update";
      
        String msg = "this is dlx msg";

        //我们设置消息过期时间，10秒后再消费 让消息进入死信队列
        AMQP.BasicProperties properties = new AMQP.BasicProperties().builder()
                .deliveryMode(2)
                .expiration("10000")
                .build();

        channel.basicPublish(exchangeName, routingKey, true, properties, msg.getBytes());
        System.out.println("Send message : " + msg);

        channel.close();
        connection.close();
    }
}
import com.rabbitmq.client.*;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class DlxConsumer {
    public static void main(String[] args) throws Exception {
    //创建连接、创建channel忽略 内容可以在上面代码中获取
        String exchangeName = "test_dlx_exchange";
        String queueName = "test_dlx_queue";
        String routingKey = "item.#";

        //必须设置参数到 arguments 中
        Map<String, Object> arguments = new HashMap<String, Object>();
        arguments.put("x-dead-letter-exchange", "dlx.exchange");

        channel.exchangeDeclare(exchangeName, "topic", true, false, null);
        //将 arguments 放入队列的声明中
        channel.queueDeclare(queueName, true, false, false, arguments);

        //一般不用代码绑定，在管理界面手动绑定
        channel.queueBind(queueName, exchangeName, routingKey);


        //声明死信队列
        channel.exchangeDeclare("dlx.exchange", "topic", true, false, null);
        channel.queueDeclare("dlx.queue", true, false, false, null);
        //路由键为 # 代表可以路由到所有消息
        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 {

                String message = new String(body, "UTF-8");
                System.out.println(" [x] Received '" + message + "'");

            }
        };

        //6. 设置 Channel 消费者绑定队列
        channel.basicConsume(queueName, true, consumer);
    }
}