通過設置每條消息的 TTL 來打造延遲隊列，本章通過 SpringBoot 演示下圖的延遲隊列架構。  <br/> 步驟如下： **1. 創建SpringBoot項目** ```xml <dependencies> <!--RabbitMQ 依賴--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-amqp</artifactId> </dependency> <!--RabbitMQ 測試依賴--> <dependency> <groupId>org.springframework.amqp</groupId> <artifactId>spring-rabbit-test</artifactId> <scope>test</scope> </dependency> <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> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.12</version> </dependency> </dependencies> ``` **3. `resources/application.properties`** ```properties spring.rabbitmq.host=192.168.0.107 spring.rabbitmq.port=5672 spring.rabbitmq.username=admin spring.rabbitmq.password=admin ``` **4. 配置類** ```java @Configuration public class MsgTtlQueueConfig { public static final String Y_DEAD_LETTER_EXCHANGE = "Y"; public static final String QUEUE_C = "QC"; /** * 隊列C綁定死信交換機Y */ @Bean("queueC") public Queue queueB() { Map<String, Object> args = new HashMap<>(16); //聲明當前隊列綁定的死信交換機 args.put("x-dead-letter-exchange", Y_DEAD_LETTER_EXCHANGE); //聲明當前隊列的死信路由key args.put("x-dead-letter-routing-key", "YD"); return QueueBuilder.durable(QUEUE_C).withArguments(args).build(); } /** * 隊列C綁定X交換機 */ @Bean public Binding queuecBindingX(@Qualifier("queueC") Queue queueC, @Qualifier("xExchange") DirectExchange xExchange) { //with(routingKey) return BindingBuilder.bind(queueC).to(xExchange).with("XC"); } } ``` **5. 生產者** ```java @Slf4j @RestController public class ProducerController { @Autowired private RabbitTemplate rabbitTemplate; @GetMapping("/msg/ttl/send") public void msgTtlSend(@RequestParam Map<String, String> params) { String message = "time: " + params.get("time") + ", message: " + params.get("message"); //convertAndSend(String exchange, String routingKey, Object message, MessagePostProcessor processor) rabbitTemplate.convertAndSend("X", "XC", message, processor -> { //設置消息的TTL processor.getMessageProperties().setExpiration(params.get("time")); return processor; }); } } ``` **6. 消費者** ```java @Slf4j @Component public class ConsumerService { @RabbitListener(queues = "QD") public void receiveD(Message message, Channel channel) throws IOException { String msg = new String(message.getBody(), "UTF-8"); log.info(msg); } } ``` **7. 測試** 啟動項目后訪問 http://localhost:8080/msg/ttl/send?time=20000&message=C1 ，生產者將生產一條消息，該消息將在 20000ms 后被消費者接收到。 ``` 2022-10-27 22:18:09.908 INFO 3184 --- [ntConsumerService : time: 20000, message: C1 ``` <br/> 如果在消息屬性上設置 TTL 的方式，消息可能并不會按時死亡，因為 RabbitMQ <mark>只會檢查第一個消息是否過期</mark>，如果過期則丟到死信隊列。<mark>如果第一個消息的延時時長很長，而第二個消息的延時時長很短，第二個消息并不會優先得到執行</mark>。如果想打造不存在這個限制的延遲隊列就需要 RabbitMQ 的[延遲插件](http://www.hmoore.net/king_om/x_1_mq/2483280)來支持了。 <br/> 如果將隊列 TTL 延遲隊列和消息 TTL 延遲隊列用在一個項目中，便可以優化為如下的架構。