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一、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。

二、死信的来源

• 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.

三、实战

1、消息 TTL 过期

生产者代码：

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)

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 directchannel.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 routingkeychannel.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 -> {});}
}

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)

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 -> {});}
}

2、队列达到最大长度

消息生产者代码去掉 TTL 属性

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)

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 directchannel.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 routingkeychannel.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");//设置正常队列长度限制params.put("x-max-length",6);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 -> {});}
}

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

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 -> {});}
}

3、消息被拒

消息生产者代码

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 消费者代码(启动之后关闭该消费者 模拟其接收不到消息)

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 directchannel.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 routingkeychannel.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 -> {});}
}

C2 消费者代码

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 -> {});}
}

启动消费者 1 然后再启动消费者 2

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总结

以上就是RabbitMQ之死信队列的相关知识点，希望对你有所帮助。