专辑：RabbitMQ专题_死信队列-Java充电社【公众号：Java充电社】

## 10.1、死信的概念

先从概念解释上搞清楚这个定义，死信，顾名思义就是无法被消费的消息，字面意思可以这样理解，一般来说， producer 将消息投递到 broker 或者直接到 queue 里了， consumer 从 queue 取出消息进行消费，但某些时候由于特定的原因导致 queue 中的某些消息无法被消费，这样的消息如果没有后续的处理，就变成了死信，有死信自然就有了死信队列。

应用场景:为了保证订单业务的消息数据不丢失，需要使用到 RabbitMQ 的死信队列机制，当消息消费发生异常时，将消息投入死信队列中；还有比如说: 用户在商城下单成功并点击去支付后在指定时间未支付时自动失效

## 10.2、死信的来源（3种）

- 消息 TTL 过期
- 队列达到最大长度(队列满了，无法再添加数据到 mq 中)
- 消息被拒绝(basic.reject 或 basic.nack)并且 requeue=false.

## 10.3、死信实战

### 1）代码架构图

![](https://itsoku.oss-cn-hangzhou.aliyuncs.com/itsoku/blog/article/388/284e4348-dedb-4ce9-a706-52dba0b774d9.png)

### 2）消息TTL过期（可实现延迟消息）

生产者代码

```java
public class Producer {
    private static final String NORMAL_EXCHANGE = "normal_exchange";

public static void main(String[] argv) throws Exception {
 try (Channel channel = RabbitMqUtils.getChannel()) {
 channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
 //设置消息的 TTL 时间
 AMQP.BasicProperties properties = new AMQP.BasicProperties().builder().expiration("10000").build();
 //该信息是用作演示队列个数限制
 for (int i = 1; i < 11; i++) {
 String message = "info" + i;
 channel.basicPublish(NORMAL_EXCHANGE, "zhangsan", properties, message.getBytes());
 System.out.println("生产者发送消息:" + message);
 }
 }
 }
}
```

消费者 C1 代码(启动之后关闭该消费者 模拟其接收不到消息)

```java
public class Consumer01 {
 //普通交换机名称
 private static final String NORMAL_EXCHANGE = "normal_exchange";
 //死信交换机名称
 private static final String DEAD_EXCHANGE = "dead_exchange";
 public static void main(String[] argv) throws Exception {
 Channel channel = RabbitUtils.getChannel();
 //声明死信和普通交换机 类型为 direct
 channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
 channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
 //声明死信队列
 String deadQueue = "dead-queue";
 channel.queueDeclare(deadQueue, false, false, false, null);
 //死信队列绑定死信交换机与 routingkey
 channel.queueBind(deadQueue, DEAD_EXCHANGE, "lisi");
 //正常队列绑定死信队列信息
 Map<String, Object> params = new HashMap<>();
 //正常队列设置死信交换机 参数 key 是固定值
 params.put("x-dead-letter-exchange", DEAD_EXCHANGE);
 //正常队列设置死信 routing-key 参数 key 是固定值
 params.put("x-dead-letter-routing-key", "lisi");
 String normalQueue = "normal-queue";
 channel.queueDeclare(normalQueue, false, false, false, params);
 channel.queueBind(normalQueue, NORMAL_EXCHANGE, "zhangsan");
 System.out.println("等待接收消息.....");
 DeliverCallback deliverCallback = (consumerTag, delivery) -> {
 String message = new String(delivery.getBody(), "UTF-8");
 System.out.println("Consumer01 接收到消息"+message);
 };
 channel.basicConsume(normalQueue, true, deliverCallback, consumerTag -> {
 });
 }
}
```

![](https://itsoku.oss-cn-hangzhou.aliyuncs.com/itsoku/blog/article/388/ae2353f1-a44c-40dd-b60f-935c9eb1bef7.png)

消费者 C2 代码(以上步骤完成后 启动 C2 消费者 它消费死信队列里面的消息)

```java
public class Consumer02 {
    private static final String DEAD_EXCHANGE = "dead_exchange";

public static void main(String[] argv) throws Exception {
        Channel channel = RabbitUtils.getChannel();
        channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
        String deadQueue = "dead-queue";
        channel.queueDeclare(deadQueue, false, false, false, null);
        channel.queueBind(deadQueue, DEAD_EXCHANGE, "lisi");
        System.out.println("等待接收死信队列消息.....");
        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            String message = new String(delivery.getBody(), "UTF-8");
            System.out.println("Consumer02 接收死信队列的消息" + message);
        };
        channel.basicConsume(deadQueue, true, deliverCallback, consumerTag -> {
        });
    }
}
```

![](https://itsoku.oss-cn-hangzhou.aliyuncs.com/itsoku/blog/article/388/b3f3a334-3f51-4ceb-a39f-8a4c1986683a.png)

### 3）队列达到最大长度

消息生产者代码去掉 TTL 属性

```java
public class Producer {
 private static final String NORMAL_EXCHANGE = "normal_exchange";
 public static void main(String[] argv) throws Exception {
 try (Channel channel = RabbitMqUtils.getChannel()) {
 channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
 //该信息是用作演示队列个数限制
 for (int i = 1; i <11 ; i++) {
 String message="info"+i;
 channel.basicPublish(NORMAL_EXCHANGE,"zhangsan",null, message.getBytes());
 System.out.println("生产者发送消息:"+message);
 }
 }
 }
}
```

C1 消费者修改以下代码(启动之后关闭该消费者 模拟其接收不到消息 )

![](https://itsoku.oss-cn-hangzhou.aliyuncs.com/itsoku/blog/article/388/2f88453d-bcc8-416c-a066-d79af7479de2.png)

注意此时需要把原先队列删除 因为参数改变了

C2 消费者代码不变(启动 C2 消费者)

![](https://itsoku.oss-cn-hangzhou.aliyuncs.com/itsoku/blog/article/388/921f0336-a055-41bb-bb24-39431b1d80d2.png)

### 4）消息拒绝

1. 消息生产者代码同上生产者一致

2. C1 消费者代码(启动之后关闭该消费者 模拟其接收不到消息)

public static void main(String[] argv) throws Exception {
 Channel channel = RabbitUtils.getChannel();
 //声明死信和普通交换机 类型为 direct
 channel.exchangeDeclare(NORMAL_EXCHANGE, BuiltinExchangeType.DIRECT);
 channel.exchangeDeclare(DEAD_EXCHANGE, BuiltinExchangeType.DIRECT);
 //声明死信队列
 String deadQueue = "dead-queue";
 channel.queueDeclare(deadQueue, false, false, false, null);
 //死信队列绑定死信交换机与 routingkey
 channel.queueBind(deadQueue, DEAD_EXCHANGE, "lisi");//正常队列绑定死信队列信息
 Map<String, Object> params = new HashMap<>();
 //正常队列设置死信交换机 参数 key 是固定值
 params.put("x-dead-letter-exchange", DEAD_EXCHANGE);
 //正常队列设置死信 routing-key 参数 key 是固定值
 params.put("x-dead-letter-routing-key", "lisi");
 String normalQueue = "normal-queue";
 channel.queueDeclare(normalQueue, false, false, false, params);
 channel.queueBind(normalQueue, NORMAL_EXCHANGE, "zhangsan");
 System.out.println("等待接收消息.....");
 DeliverCallback deliverCallback = (consumerTag, delivery) -> {
 String message = new String(delivery.getBody(), "UTF-8");
 if (message.equals("info5")) {
 System.out.println("Consumer01 接收到消息" + message + "并拒绝签收该消息");
 //requeue 设置为 false 代表拒绝重新入队 该队列如果配置了死信交换机将发送到死信队列中
 channel.basicReject(delivery.getEnvelope().getDeliveryTag(), false);
 } else {
 System.out.println("Consumer01 接收到消息" + message);
 channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
 }
 };
 boolean autoAck = false;
 channel.basicConsume(normalQueue, autoAck, deliverCallback, consumerTag -> {
 });
 }
}
```

![](https://itsoku.oss-cn-hangzhou.aliyuncs.com/itsoku/blog/article/388/b18b28ef-aaa0-4a1e-ab42-cd043568319a.png)

C2 消费者代码不变，启动消费者 1，然后再启动消费者 2

![](https://itsoku.oss-cn-hangzhou.aliyuncs.com/itsoku/blog/article/388/6800be83-8c09-4449-bba3-5fd82414e735.png)

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