背景

        RabbitMQ死信队列俗称，备胎队列；消息中间件因为某种原因拒收该消息后，可以转移到死信队列中存放，死信队列也可以有交换机和路由key等。

原理

        死信队列和普通队列区别不是很大

        普通与死信队列都有自己独立的交换机和路由key、队列和消费者。

区别：

        1.生产者投递消息先投递到我们普通交换机中，普通交换机在将该消息投到

普通队列中缓存起来，普通队列对应有自己独立普通消费者。

        2.如果生产者投递消息到普通队列中，普通队列发现该消息一直没有被消费者消费

的情况下，在这时候会将该消息转移到死信（备胎）交换机中，死信（备胎）交换机

对应有自己独立的 死信（备胎）队列 对应独立死信（备胎）消费者。

普通队列中，普通队列发现该消息一直没有被消费者消费

的情况下，在这时候会将该消息转移到死信（备胎）交换机中，死信（备胎）交换机

对应有自己独立的 死信（备胎）队列 对应独立死信（备胎）消费者。

产生死信队列的原因

工具类：

public class RabbitMqUtils {     //得到一个连接的 channel     public static Channel getChannel() throws Exception{         //创建一个连接工厂         ConnectionFactory factory = new ConnectionFactory();         factory.setHost("127.0.0.1");         factory.setUsername("guest");         factory.setPassword("guest");         //创建连接         Connection connection = factory.newConnection();         //创建通道         Channel channel = connection.createChannel();         return channel;     } }

1. 消息投递到MQ中存放 消息已经过期  消费者没有及时的获取到我们消息，消息如果存放到mq服务器中过期之后，会转移到备胎死信队列存放。

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);             }         }     } }

消费端：

普通消费：

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 = RabbitMqUtils.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 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 -> {         });     } }

死信消费：

public class Consumer02 {     private static final String DEAD_EXCHANGE = "dead_exchange";     public static void main(String[] argv) throws Exception {         Channel channel = RabbitMqUtils.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 -> {         });     } }

运行结果查询:

  1.启动消费端->启动死信队列->启动生产者 查看结果

  2.关闭消费端->启动生产者 再次查看结果    结果原因：消费端队列关闭，消息时间过期会进入死信队列

2. 队列达到最大的长度 （队列容器已经满了）

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);             }         }     } }

消费端：

普通消费：

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 = RabbitMqUtils.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 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");         params.put("x-max-length",6); //设置队列长度为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 -> {         });     } } 

死信消费：

public class Consumer02 {     private static final String DEAD_EXCHANGE = "dead_exchange";     public static void main(String[] argv) throws Exception {         Channel channel = RabbitMqUtils.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 -> {         });     } }

运行结果查询:

  1.启动消费端->启动死信队列->启动生产者 查看结果

         结果原因：消费端队列只能存储6条消息,剩下的消息进入死信队列

3. 消费者消费多次消息失败，就会转移存放到死信队列中

注意：与其他不同的是，需要开启手动应答 

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);             }         }     } }

消费端：

普通消费：

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 = RabbitMqUtils.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 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 -> {         });     } }

死信消费：

public class Consumer02 {     private static final String DEAD_EXCHANGE = "dead_exchange";     public static void main(String[] argv) throws Exception {         Channel channel = RabbitMqUtils.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 -> {         });     } }

运行结果查询:

  1.启动消费端->启动死信队列->启动生产者 查看结果

         结果原因：消费端队列消息中为info5时,消费端拒绝签收,只能进入死信队列