Spring Boot Event 事件实现异步延迟执行

Spring Boot 利用DelayQueue实现延迟执行事件Event

peak_paradise

7089人浏览 · 2022-05-13 10:01:31

peak_paradise · 2022-05-13 10:01:31 发布

Spring的事件（Application Event）非常好用，虽然有一点会出现代码污染，但是在做不使用其他框架来做异步的情况先，还是非常方便的。使用它只需要三样东西

自定义事件：继承 ApplicationEvent，创建一个你想传的数据的对象，会在监听器那边收到该对象。
定义监听器，实现 ApplicationListener 或者通过 @EventListener 注解到方法上，两种方式都行，但是推荐使用@EventListener，只要参数是你写的继承ApplicationEvent的对象，就会自动找到执行方法。
定义发布者，通过 ApplicationEventPublisher，自带的bean，不需要单独声明，直接@Autowired就能使用，主要只需要publishEvent方法。

但是有时候我需要做延时执行，自带的功能缺不支持，但是我发现ApplicationEvent对象里面有两个成员变量，source和timestamp，构造函数（@since 5.3.8）也提供了同时注入这两个变量数据。

   /**
	 * Create a new {@code ApplicationEvent} with its {@link #getTimestamp() timestamp}
	 * set to the value returned by {@link Clock#millis()} in the provided {@link Clock}.
	 * <p>This constructor is typically used in testing scenarios.
	 * @param source the object on which the event initially occurred or with
	 * which the event is associated (never {@code null})
	 * @param clock a clock which will provide the timestamp
	 * @since 5.3.8
	 * @see #ApplicationEvent(Object)
	 */
	public ApplicationEvent(Object source, Clock clock) {
		super(source);
		this.timestamp = clock.millis();
	}

但是，看了说明timestamp只是标志执行的时间，并不是为了延迟执行，可惜了。于是查了一些资料，找到java.util.concurrent.DelayQueue对象，JDK自带了延迟的队列对象，我们可以考虑利用自带的timestamp和延迟队列DelayQueue结合一起来实现，具体DelayQueue的使用请自行查询，非常的简单。

首先，继承的ApplicationEvent重新实现一下。不单单要继承ApplicationEvent，还需要实现Delayed，主要是因为DelayQueue队列中必须是Delayed的实现类

import java.time.Clock;
import java.time.Duration;
import java.util.Date;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

import org.springframework.context.ApplicationEvent;

import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.extern.slf4j.Slf4j;

@Data
@EqualsAndHashCode(callSuper = false)
public class ApplicationDelayedEvent extends ApplicationEvent implements Delayed {

	private static final long serialVersionUID = 1L;

	public ApplicationDelayedEvent(Object source) {
		this(source, 0L);
	}

	public ApplicationDelayedEvent(Object source, long delaySeconds) {
		super(source, Clock.offset(Clock.systemDefaultZone(), Duration.ofSeconds(delaySeconds)));
	}

	@Override
	public int compareTo(Delayed o) {
		// 最好用NANOSECONDS，更精确，但是用处不大
		long delta = getDelay(TimeUnit.MILLISECONDS) - o.getDelay(TimeUnit.MILLISECONDS);
		return (int) delta;
	}

	@Override
	public long getDelay(TimeUnit unit) {
		// 最好用NANOSECONDS，更精确，但是用处不大，负数也会认为到时间了
		long millis = this.getTimestamp();
		long currentTimeMillis = System.currentTimeMillis();
		long sourceDuration = millis - currentTimeMillis;
		return unit.convert(sourceDuration, unit);
	}
}

多了两个必须实现的方法，compareTo是排序，应该是队列中的顺序。getDelay是主要的方法，目的是归0的时候会从DelayQueue释放出来，当然那必须是NANOSECONDS级别的，我使用MILLISECONDS，就会出现负数，但也是可以的，也能释放出来。

另一个需要改的就是发布者，所以重新写一个ApplicationDelayEventPublisher

import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.util.concurrent.DelayQueue;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.stereotype.Component;

import lombok.extern.slf4j.Slf4j;

@Slf4j
@Component
public class ApplicationDelayEventPublisher implements ApplicationRunner {

	// ApplicationDelayedEvent需要import进来
	private DelayQueue<ApplicationDelayedEvent> delayQueue = new DelayQueue<>();

	@Autowired
	private ApplicationEventPublisher eventPublisher;

	@Autowired
    @Qualifier("watchTaskExecutor")
	private ThreadPoolTaskExecutor poolTaskExecutor;

	public void publishEvent(ApplicationDelayedEvent event) {
		boolean result = delayQueue.offer(event);
		log.info("加入延迟队列。。。。{}", result);
	}

	@Override
	public void run(ApplicationArguments args) throws Exception {
		poolTaskExecutor.execute(() -> watchThread());
	}

	private void watchThread() {
		while (true) {
			try {
				log.info("启动延时任务的监听线程。。。。");
				ApplicationDelayedEvent event = this.delayQueue.take();
				log.info("接收到延时任务执行。。。{}", ZonedDateTime.now().format(DateTimeFormatter.ISO_OFFSET_DATE_TIME));
				eventPublisher.publishEvent(event);
			} catch (InterruptedException e) {
				log.info("启动延时任务的监听线程关闭");
				this.delayQueue.clear();
				break;
			}
		}
	}
}

需要实现ApplicationRunner作为Spring boot的启动时候运行的bean，目的就是开启监听线程，有事件到了执行时间take方法会得到数据，然后调用Spring原生的事件发布。

另外特别说明的就是监听线程不能随便创建，脱离了Spring容器的线程池会造成关闭服务的时候造成无法关闭的现象，所以建议还是自定义一个ThreadPoolTaskExecutor

    @Bean
	public ThreadPoolTaskExecutor watchTaskExecutor() {
		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
		executor.setCorePoolSize(1);
		executor.setMaxPoolSize(1);
		executor.setQueueCapacity(1);
		executor.setKeepAliveSeconds(60);
		executor.setThreadNamePrefix("watch_task_");

		// 线程池对拒绝任务的处理策略
//		ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常
//		ThreadPoolExecutor.DiscardPolicy：丢弃任务，但是不抛出异常。
//		ThreadPoolExecutor.DiscardOldestPolicy：丢弃队列最前面。
//		ThreadPoolExecutor.CallerRunsPolicy：由调用者处理该任务 。
		executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
		// 初始化
		executor.initialize();
		return executor;
	}

最后就是接收事件，跟传统的接收是一样的，异步只需要在配置类上加上@EnableAsync注解就行了，然后在监听的方法上加@Async

import java.util.concurrent.ThreadPoolExecutor;

import javax.annotation.PostConstruct;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;

import lombok.extern.slf4j.Slf4j;

@Slf4j
@Configuration
@EnableAsync
@ConditionalOnClass(ApplicationDelayEventPublisher.class)
public class DelayEventConfiguration {

	@PostConstruct
	public void init() {
		log.info("延迟Spring事件模块启动中。。。");
	}
    
    // 不能和监听线程放到一个线程池，不然无法执行
	@Bean
	public ThreadPoolTaskExecutor poolTaskExecutor() {
		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
		executor.setCorePoolSize(3);
		executor.setMaxPoolSize(50);
		executor.setQueueCapacity(10000);
		executor.setKeepAliveSeconds(30);
		executor.setThreadNamePrefix("my_task_");

		// 线程池对拒绝任务的处理策略
//		ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常
//		ThreadPoolExecutor.DiscardPolicy：丢弃任务，但是不抛出异常。
//		ThreadPoolExecutor.DiscardOldestPolicy：丢弃队列最前面。
//		ThreadPoolExecutor.CallerRunsPolicy：由调用者处理该任务 。
		executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());
		// 初始化
		executor.initialize();
		return executor;
	}
    
    @Bean
	public ThreadPoolTaskExecutor watchTaskExecutor() {
		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
		executor.setCorePoolSize(1);
		executor.setMaxPoolSize(1);
		executor.setQueueCapacity(1);
		executor.setKeepAliveSeconds(60);
		executor.setThreadNamePrefix("watch_task_");

		// 线程池对拒绝任务的处理策略
//		ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常
//		ThreadPoolExecutor.DiscardPolicy：丢弃任务，但是不抛出异常。
//		ThreadPoolExecutor.DiscardOldestPolicy：丢弃队列最前面。
//		ThreadPoolExecutor.CallerRunsPolicy：由调用者处理该任务 。
		executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
		// 初始化
		executor.initialize();
		return executor;
	}
}

	@Async("poolTaskExecutor")
	@EventListener
	public void listenDelayEvent(ApplicationDelayedEvent event) {
		log.info("收到执行事件：{}", event.getSource());
	}