SpringBoot【注解 01】@Scheduled实现定时任务的串行和并行执行

在SpringBoot中，如果使用@Scheduled注解来定义多个定时任务，默认情况下这些任务将会被安排在一个单线程的调度器中执行。这意味着，这些任务将会串行执行，而不是并行执行。当一个任务正在执行时，其他被触发的任务将会等待当前任务完成后再开始执行，这可能导致任务执行上的阻塞，特别是当某个任务执行时间较长时，可能会延迟后续任务的启动时间，影响定时任务的准时性。

1.问题代码及测试结果

问题代码：

    @Scheduled(cron = "*/1 * * * * *")public void a() throws InterruptedException {log.info("A Start {}!", System.currentTimeMillis());Thread.sleep(2000);log.info("A End {}!", System.currentTimeMillis());}@Scheduled(cron = "*/1 * * * * *")public void b() {log.info("B Start {}!", System.currentTimeMillis());log.info("B End {}!", System.currentTimeMillis());}

部分测试结果：

15:38:29.001 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716968309001!
15:38:29.001 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716968309001!
15:38:29.001 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716968309001!15:38:31.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716968311003!
15:38:31.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716968311003!
15:38:31.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716968311003!15:38:32.002 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716968312002!15:38:34.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716968314003!
15:38:34.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716968314003!
15:38:34.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716968314003!

结果分析：

• A和B是串行的。

2.定时任务实现并行

2.1 使用自定义线程池（添加类）

可以通过配置一个自定义的TaskScheduler或者ThreadPoolTaskScheduler来为@Scheduled任务提供一个线程池，从而允许多个任务并行执行。例如，可以在配置类中定义一个ThreadPoolTaskScheduler Bean：

@Configuration
public class AsyncConfig {@Beanpublic ThreadPoolTaskScheduler taskScheduler() {ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();// 设置线程池大小scheduler.setPoolSize(10); scheduler.setThreadNamePrefix("my-scheduled-task-");return scheduler;}
}

并确保你的配置类被扫描到，且在@EnableScheduling注解的上下文中。
测试代码：

@Scheduled(cron = "*/1 * * * * *")public void a() throws InterruptedException {log.info("A Start {}!", System.currentTimeMillis());Thread.sleep(2000);log.info("A End {}!", System.currentTimeMillis());}@Scheduled(cron = "*/1 * * * * *")public void b() {log.info("B Start {}!", System.currentTimeMillis());log.info("B End {}!", System.currentTimeMillis());}

部分测试结果：

15:16:18.003 [my-scheduled-task-2] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716966978003!
15:16:18.003 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966978003!
15:16:18.003 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966978003!15:16:19.002 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966979002!
15:16:19.002 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966979002!15:16:20.004 [my-scheduled-task-2] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716966980004!
15:16:20.004 [my-scheduled-task-3] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966980004!
15:16:20.004 [my-scheduled-task-3] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966980004!15:16:21.003 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716966981003!
15:16:21.003 [my-scheduled-task-4] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966981003!
15:16:21.003 [my-scheduled-task-4] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966981003!15:16:22.001 [my-scheduled-task-2] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966982001!
15:16:22.001 [my-scheduled-task-2] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966982001!15:16:23.004 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716966983004!
15:16:23.004 [my-scheduled-task-3] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966983004!
15:16:23.004 [my-scheduled-task-3] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966983004!

结果分析：

• A和B是并行的；
• A和A或者B和B是串行的。

2.2 使用异步处理（添加类和注解）

结合@Async注解和@EnableAsync可以使得每个@Scheduled任务在独立的线程中异步执行。
首先需要在配置类中启用异步支持，并配置一个线程池，然后在每个定时任务方法上添加@Async注解。

@EnableAsync
@Configuration
public class AsyncConfig {@Beanpublic Executor taskExecutor() {ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();executor.setCorePoolSize(10);executor.setMaxPoolSize(20);executor.setQueueCapacity(200);executor.setThreadNamePrefix("Async-");executor.initialize();return executor;}
}

测试代码：

    @Async@Scheduled(cron = "*/1 * * * * *")public void a() throws InterruptedException {log.info("A Start {}!", System.currentTimeMillis());Thread.sleep(2000);log.info("A End {}!", System.currentTimeMillis());}@Async@Scheduled(cron = "*/1 * * * * *")public void b() {log.info("B Start {}!", System.currentTimeMillis());log.info("B End {}!", System.currentTimeMillis());}

部分测试结果：

15:26:52.008 [Async-2] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967612008!
15:26:52.008 [Async-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967612008!
15:26:52.009 [Async-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967612009!15:26:53.002 [Async-4] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967613002!
15:26:53.002 [Async-3] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967613002!
15:26:53.002 [Async-3] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967613002!15:26:54.001 [Async-6] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967614001!
15:26:54.001 [Async-5] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967614001!
15:26:54.001 [Async-5] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967614001!
15:26:54.010 [Async-2] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716967614010!15:26:55.002 [Async-8] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967615002!
15:26:55.002 [Async-7] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967615002!
15:26:55.002 [Async-7] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967615002!
15:26:55.002 [Async-4] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716967615002!15:26:56.001 [Async-10] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967616001!
15:26:56.001 [Async-9] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967616001!
15:26:56.001 [Async-9] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967616001!
15:26:56.002 [Async-6] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716967616002!15:26:57.001 [Async-3] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967617001!
15:26:57.001 [Async-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967617001!
15:26:57.001 [Async-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967617001!
15:26:57.002 [Async-8] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716967617002!

测试结果分析：

• A和B是并行的；
• A和A或者B和B也是并行的。

3.总结

如有错误，请小伙伴儿们不吝赐教。
定时任务有不同的需求，使用串行还是并行要结合业务进行选择。