1 简介

TTL：
time to live 消息存活时间，如果消息在存活时间内未被消费，则会别清除。 RabbitMQ⽀持两种ttl设置，单独消息进⾏配置ttl，整个队列进⾏配置ttl（居多）。

死信队列：
没有被及时消费的消息存放的队列。

死信交换机：
Dead Letter Exchange（死信交换机，缩写：DLX）当消息成为死信后，会被重新发送到另⼀个交换机，这个交换机就是DLX死信交换机。

消息成为死信的条件：

(1) 消费者拒收消息（basic.reject/ basic.nack），并且没有重新⼊队 requeue=false。
(2) 消息在队列中未被消费，且超过队列或者消息本身的过期时间TTL(time-to-live)。
(3) 队列的消息⻓度达到极限。

消息成为死信后，如果该队列绑定了死信交换机，则消息会被死信交换机重新路由到死信队列。

PS： 死信队列、死信交换机和普通队列、普通交换机没有区别。

2 死信队列代码实现

2.1 pom

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.0.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <java.version>1.8</java.version>
    </properties>


    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!--日志-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-logging</artifactId>
        </dependency>
        <!--rabbitmq-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-amqp</artifactId>
        </dependency>
        <!--公用包-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.71</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-collections4</artifactId>
            <version>4.2</version>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
        </dependency>

    </dependencies>


    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.3.0.RELEASE</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

2.2 application.yml

server:
  port: 8080

spring:
  rabbitmq:
    host: 192.168.38.80
    port: 5672
    username: guest
    password: guest
    virtual-host: /
    listener:
      simple:
        #手动确认
        acknowledge-mode: manual

2.3 RabbitMqConsts

public final class RabbitMqConsts {

    private RabbitMqConsts() {

    }


    public static final String BUSINESS_EXCHANGE_NAME = "business_exchange";

    public static final String BUSINESS_ROUTING_KEY = "business_routing_key";

    public static final String DEAD_EXCHANGE_NAME = "dead_exchange";

    public static final String BUSINESS_QUEUE = "business_queue";

    public static final String DEAD_QUEUE = "dead_queue";

    public static final String DEAD_ROUTING_KEY = "dead_routing_key";


}

2.4 DeadRabbitMqConfig

@Configuration
public class DeadRabbitMqConfig {


    /**
     * 业务交换机
     */
    @Bean
    public Exchange businessExchange() {
        return new DirectExchange(RabbitMqConsts.BUSINESS_EXCHANGE_NAME);
    }


    /**
     *  业务队列
     */
    @Bean
    public Queue businessQueue() {
        //绑定死信交换机
        Map<String, Object> paramMap = new HashMap<>();
        paramMap.put("x-dead-letter-exchange", RabbitMqConsts.DEAD_EXCHANGE_NAME);
        paramMap.put("x-dead-letter-routing-key", RabbitMqConsts.DEAD_ROUTING_KEY);
        //当前消息过期时间为5秒
        paramMap.put("x-message-ttl", 5000);
        return QueueBuilder.durable(RabbitMqConsts.BUSINESS_QUEUE).withArguments(paramMap).build();
    }


    @Bean
    public Binding businessBind(@Qualifier("businessQueue") Queue queue,
                                @Qualifier("businessExchange") Exchange exchange) {

        return BindingBuilder.bind(queue).to(exchange).with(RabbitMqConsts.BUSINESS_ROUTING_KEY).noargs();
    }

    /**
     *  死信交换机
     */
    @Bean
    public Exchange deadExchange() {
        return new DirectExchange(RabbitMqConsts.DEAD_EXCHANGE_NAME);
    }

    /**
     *  死信队列
     */
    @Bean
    public Queue deadQueue() {
        return QueueBuilder.durable(RabbitMqConsts.DEAD_QUEUE).build();
    }

    /**
     * 绑定死信交换机和死信队列
     */
    @Bean
    public Binding deadBing(@Qualifier("deadExchange") Exchange exchange, @Qualifier("deadQueue") Queue queue) {

        return BindingBuilder.bind(queue).to(exchange).with(RabbitMqConsts.DEAD_ROUTING_KEY).noargs();
    }


}

2.5 RabbitmqConsumer

描述： 死信消费者。

@Component
@RabbitListener(queues = RabbitMqConsts.DEAD_QUEUE)
@Slf4j
public class RabbitmqConsumer {


    @RabbitHandler
    public void receiveMessage(Message message, String body, Channel channel) throws IOException {
        System.out.println("死信队列接收到消息：" + body);
        channel.basicAck(message.getMessageProperties().getDeliveryTag(), false);
    }

}

2.6 ProviderController

@RestController
@RequestMapping("/provider")
@Slf4j
public class ProviderController {


    @Autowired
    private RabbitTemplate rabbitTemplate;


    @GetMapping("/send")
    public String send() {
        String message = "Hello SpringBoot RabbitMq";
        rabbitTemplate.convertAndSend(RabbitMqConsts.BUSINESS_EXCHANGE_NAME, RabbitMqConsts.BUSINESS_ROUTING_KEY, message );
        return "发送成功";
    }



}

2.7 启动类

@SpringBootApplication
public class RabbitmqApplication {

    public static void main(String[] args) {

        SpringApplication.run(RabbitmqApplication.class);

    }

}

2.8 测试

结果： 消息发送到业务队列，队列中消息存活时间为5S，超过5S未被消费，消息进入死信队列，消费端监听死信队列消息。

描述： 过5秒后