延遲隊列的使用場景還比較多，例如：

1、超時未收到支付回調，主動查詢支付狀態；

2、規定時間內，訂單未支付，自動取消；

。。。

總之，但凡需要在未來的某個確定的時間點執行檢查的場景中都可以用延遲隊列。

常見的手段主要有：定時任務掃描、RocketMQ延遲隊列、Java自動的延遲隊列、監聽Redis Key過期等等

首先，定義一個延遲任務

package com.cjs.example;import lombok.Data;import java.util.concurrent.Delayed;import java.util.concurrent.TimeUnit;/** * @author ChengJianSheng * @since 2021/3/18 */@Datapublic class DelayTask implements Delayed { private Long orderId; private long expireTime; public DelayTask(Long orderId, long expireTime) { this.orderId = orderId; this.expireTime = expireTime; } @Override public long getDelay(TimeUnit unit) { return expireTime - System.currentTimeMillis(); } @Override public int compareTo(Delayed o) { return (int) (getDelay(TimeUnit.MILLISECONDS) - o.getDelay(TimeUnit.MILLISECONDS)); }}

然后，定義一個管理類

package com.cjs.example;import lombok.extern.slf4j.Slf4j;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.boot.CommandLineRunner;import org.springframework.stereotype.Component;import java.util.concurrent.DelayQueue;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;/** * @author ChengJianSheng * @since 2021/3/19 */@Slf4j@Componentpublic class DelayQueueManager implements CommandLineRunner { private DelayQueue<DelayTask> queue = new DelayQueue<>(); @Autowired private ParkOrderQueryHandler handler; @Override public void run(String... strings) throws Exception { ExecutorService executorService = Executors.newSingleThreadExecutor(); executorService.execute(new Runnable() { @Override public void run() { while (true) { try { DelayTask task = queue.take(); handler.handle(task); } catch (InterruptedException e) { e.printStackTrace(); } } } }); } public void put(DelayTask task) { queue.put(task); }}

插入任務

@Slf4j@Servicepublic class PayServiceImpl implements PayService { @Autowired private DelayQueueManager delayQueueManager; @Override public void pay() { delayQueueManager.put(new DelayTask(1, 15)); delayQueueManager.put(new DelayTask(2, 30)); delayQueueManager.put(new DelayTask(3, 60)); }}2. Redis Key過期回調

修改redis.conf文件

# bind 127.0.0.1 -::1protected-mode nonotify-keyspace-events Ex

[root@localhost redis-6.2.1]$ src/redis-server redis.conf <?xml version='1.0' encoding='UTF-8'?><project xmlns='http://maven.apache.org/POM/4.0.0' xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance' xsi:schemaLocation='http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd'> <modelVersion>4.0.0</modelVersion> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.4.4</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.example</groupId> <artifactId>demo0401</artifactId> <version>0.0.1-SNAPSHOT</version> <name>demo0401</name> <description>Demo project for Spring Boot</description> <properties> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build></project>

RedisConfig.java

package com.example.config;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.data.redis.connection.RedisConnectionFactory;import org.springframework.data.redis.listener.RedisMessageListenerContainer;/** * @author ChengJianSheng * @since 2021/4/2 */@Configurationpublic class RedisConfig { @Bean public RedisMessageListenerContainer container(RedisConnectionFactory connectionFactory) { RedisMessageListenerContainer container = new RedisMessageListenerContainer(); container.setConnectionFactory(connectionFactory); return container; }}

創建一個監聽類

package com.example.listener;import org.springframework.data.redis.connection.Message;import org.springframework.data.redis.listener.KeyExpirationEventMessageListener;import org.springframework.data.redis.listener.RedisMessageListenerContainer;import org.springframework.stereotype.Component;/** * @author ChengJianSheng * @since 2021/4/2 */@Componentpublic class MyRedisKeyExpirationListener extends KeyExpirationEventMessageListener { public MyRedisKeyExpirationListener(RedisMessageListenerContainer listenerContainer) { super(listenerContainer); } @Override public void onMessage(Message message, byte[] pattern) { String expiredKey = message.toString(); System.out.println('監聽到Key: ' + expiredKey + ' 已過期'); }}3. RocketMQ

官方文檔：https://help.aliyun.com/document_detail/29549.htm

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