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