spring自带的定时任务功能@EnableScheduling

Posted 2020-12-27 老人与JAVA

1 demo

package com.test.domi.config;

import org.springframework.beans.factory.annotation.Configurable;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
import java.text.SimpleDateFormat;
import java.util.Date;

@Component
@Configurable
@EnableScheduling
public class ScheduledTasks {
    //每30秒执行一次
    @Scheduled(fixedRate = 1000 * 30)
    public void reportCurrentTime(){
        System.out.println ("Scheduling Tasks Examples: The time is now " + dateFormat ().format (new Date ()));
    }

    //在固定时间执行
    @Scheduled(cron = "0 */1 *  * * * ")
    public void reportCurrentByCron(){
        System.out.println ("Scheduling Tasks Examples By Cron: The time is now " + dateFormat ().format (new Date()));
    }

    private SimpleDateFormat dateFormat(){
        return new SimpleDateFormat ("HH:mm:ss");
    }
}

Scheduling Tasks Examples: The time is now 11:55:54
Scheduling Tasks Examples By Cron: The time is now 11:56:00
Scheduling Tasks Examples: The time is now 11:56:24
Scheduling Tasks Examples: The time is now 11:56:54
Scheduling Tasks Examples By Cron: The time is now 11:57:00

 

2 详解

http://tramp.cincout.cn/2017/08/18/spring-task-2017-08-18-spring-boot-enablescheduling-analysis/

cron表达式：https://www.zhyd.me/article/43

 

3 总结

默认的 ConcurrentTaskScheduler 计划执行器采用Executors.newSingleThreadScheduledExecutor() 实现单线程的执行器。因此，对同一个调度任务的执行总是同一个线程。如果任务的执行时间超过该任务的下一次执行时间，则会出现任务丢失，跳过该段时间的任务。上述问题有以下解决办法：

采用异步的方式执行调度任务，配置 Spring 的 @EnableAsync，在任务执行的方法上标注 @Async配置任务执行池，采用 ThreadPoolTaskScheduler.setPoolSize(n)。 n 的数量为 单个任务执行所需时间 / 任务执行的间隔时间