SpringBoot源码分析之@Scheduled

Springboot写上注解@Scheduled就可以实现定时任务，

这里对其源码做一点分析

@Service
public class MyScheduled {@Scheduled(cron="${time.cron}")void paoapaoScheduled() {System.out.println("Execute at " + System.currentTimeMillis());}
}

配置文件100秒一次

time.cron=*/100 * * * * *

重要的类ScheduledAnnotationBeanPostProcessor

@Nullableprivate BeanFactory beanFactory;

private void finishRegistration() {if (this.scheduler != null) {this.registrar.setScheduler(this.scheduler);}if (this.beanFactory instanceof ListableBeanFactory) {Map<String, SchedulingConfigurer> beans =((ListableBeanFactory) this.beanFactory).getBeansOfType(SchedulingConfigurer.class);List<SchedulingConfigurer> configurers = new ArrayList<>(beans.values());AnnotationAwareOrderComparator.sort(configurers);for (SchedulingConfigurer configurer : configurers) {configurer.configureTasks(this.registrar);}}if (this.registrar.hasTasks() && this.registrar.getScheduler() == null) {Assert.state(this.beanFactory != null, "BeanFactory must be set to find scheduler by type");try {// Search for TaskScheduler bean...this.registrar.setTaskScheduler(resolveSchedulerBean(this.beanFactory, TaskScheduler.class, false));}catch (NoUniqueBeanDefinitionException ex) {logger.trace("Could not find unique TaskScheduler bean", ex);try {this.registrar.setTaskScheduler(resolveSchedulerBean(this.beanFactory, TaskScheduler.class, true));}catch (NoSuchBeanDefinitionException ex2) {if (logger.isInfoEnabled()) {logger.info("More than one TaskScheduler bean exists within the context, and " +"none is named 'taskScheduler'. Mark one of them as primary or name it 'taskScheduler' " +"(possibly as an alias); or implement the SchedulingConfigurer interface and call " +"ScheduledTaskRegistrar#setScheduler explicitly within the configureTasks() callback: " +ex.getBeanNamesFound());}}}catch (NoSuchBeanDefinitionException ex) {logger.trace("Could not find default TaskScheduler bean", ex);// Search for ScheduledExecutorService bean next...try {this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, false));}catch (NoUniqueBeanDefinitionException ex2) {logger.trace("Could not find unique ScheduledExecutorService bean", ex2);try {this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, true));}catch (NoSuchBeanDefinitionException ex3) {if (logger.isInfoEnabled()) {logger.info("More than one ScheduledExecutorService bean exists within the context, and " +"none is named 'taskScheduler'. Mark one of them as primary or name it 'taskScheduler' " +"(possibly as an alias); or implement the SchedulingConfigurer interface and call " +"ScheduledTaskRegistrar#setScheduler explicitly within the configureTasks() callback: " +ex2.getBeanNamesFound());}}}catch (NoSuchBeanDefinitionException ex2) {logger.trace("Could not find default ScheduledExecutorService bean", ex2);// Giving up -> falling back to default scheduler within the registrar...logger.info("No TaskScheduler/ScheduledExecutorService bean found for scheduled processing");}}}this.registrar.afterPropertiesSet();}

bean

找到自定义的MyScheduled

这里先逆向找到可见代码，再往上找到他的赋值地方

if (this.registrar.hasTasks() && this.registrar.getScheduler() == null) {Assert.state(this.beanFactory != null, "BeanFactory must be set to find scheduler by type");try {// Search for TaskScheduler bean...this.registrar.setTaskScheduler(resolveSchedulerBean(this.beanFactory, TaskScheduler.class, false));}catch (NoUniqueBeanDefinitionException ex) {logger.trace("Could not find unique TaskScheduler bean", ex);try {this.registrar.setTaskScheduler(resolveSchedulerBean(this.beanFactory, TaskScheduler.class, true));}

重要类ScheduledThreadPoolExecutor

参考：https://www.jianshu.com/p/502f9952c09b

ScheduledThreadPoolExecutor继承了ThreadPoolExecutor，也就是说ScheduledThreadPoolExecutor拥有execute()和submit()提交异步任务的基础功能，ScheduledThreadPoolExecutor类实现了ScheduledExecutorService，该接口定义了ScheduledThreadPoolExecutor能够延时执行任务和周期执行任务的功能。

ScheduledThreadPoolExecutor也两个重要的内部类：DelayedWorkQueue和ScheduledFutureTask。可以看出DelayedWorkQueue实现了BlockingQueue接口，也就是一个阻塞队列，ScheduledFutureTask则是继承了FutureTask类，也表示该类用于返回异步任务的结果。

/*** @throws RejectedExecutionException {@inheritDoc}* @throws NullPointerException       {@inheritDoc}*/public ScheduledFuture<?> schedule(Runnable command,long delay,TimeUnit unit) {if (command == null || unit == null)throw new NullPointerException();RunnableScheduledFuture<?> t = decorateTask(command,new ScheduledFutureTask<Void>(command, null,triggerTime(delay, unit)));delayedExecute(t);return t;}

到了schedule这里：

增加定时任务ScheduledTaskRegistrar

protected void scheduleTasks() {if (this.taskScheduler == null) {this.localExecutor = Executors.newSingleThreadScheduledExecutor();this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);}if (this.triggerTasks != null) {for (TriggerTask task : this.triggerTasks) {addScheduledTask(scheduleTriggerTask(task));}}if (this.cronTasks != null) {for (CronTask task : this.cronTasks) {addScheduledTask(scheduleCronTask(task));}}if (this.fixedRateTasks != null) {for (IntervalTask task : this.fixedRateTasks) {addScheduledTask(scheduleFixedRateTask(task));}}if (this.fixedDelayTasks != null) {for (IntervalTask task : this.fixedDelayTasks) {addScheduledTask(scheduleFixedDelayTask(task));}}}

遍历arrayList

跳出refresh

Spring如何添加钩子函数

这里没有注册钩子函数自然是null

进Runtime.getRuntime().addShutdownHook(this.shutdownHook);

终于完了

============================

触发定时

倒着看就知道怎么调用的，实际上是反射执行上述方法的：

invoke方法用来在运行时动态地调用某个实例的方法

这里实行了Runnable 接口：

反射，线程，线程池 底层还是这些技术！需要好好研究这块代码，加深理解基本原理。

扩展信息：SpringBoot中定时任务默认是串行执行 如何设置并行

SpringBoot 使用@Scheduled注解配置串行、并行定时任务

Spring Boot 中实现定时任务的两种方式