怎么实现Java中的延迟队列？

在我们日常生活中，延迟队列的应用场景有很多，例如超时未受到支付回调，主动查询支付状态；规定之间内，订单未支付，自动取消等等。今天我们将会介绍几种Java中延迟队列常用到的实现方法。

常见的实现方法主要有：定时任务扫描、RocketMQ延迟队列、Java自动的延迟队列、监听Redis Key过期等等

1.  DelayQueue

首先，定义一个延迟任务

package com.cjs.example;

import lombok.Data;

import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

/**
 * @author ChengJianSheng
 * @since 2021/3/18
 */
@Data
public 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，定义一个管理类

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
@Component
public 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);
 }
}

插入任务

@Slf4j
@Service
public 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过期回调

修改redis.conf文件

# bind 127.0.0.1 -::1
protected-mode no
notify-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
 */
@Configuration
public class RedisConfig {

 @Bean
 public RedisMessageListenerContainer container(RedisConnectionFactory connectionFactory) {
  RedisMessageListenerContainer container = new RedisMessageListenerContainer();
  container.setConnectionFactory(connectionFactory);
  return container;
 }
}

创建一个监听类

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
 */
@Component
public 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("监听到Key: " + expiredKey + " 已过期");
 }
}

3.  RocketMQ

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

关于Java延迟队列的应用场景和相关实现方法就介绍到此，想要了解更多关于Java 延迟队列实现方式的资料请关注W3Cschool其它相关文章！