Springboot寫上注解@Scheduled就可以實現定時任務，

這里對其源碼做一點分析

@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 * * * * *

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重要的類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?

找到自定義的MyScheduled

這里先逆向找到可見代碼，再往上找到他的賦值地方

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));}

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重要類ScheduledThreadPoolExecutor

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

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ScheduledThreadPoolExecutor繼承了ThreadPoolExecutor，也就是說ScheduledThreadPoolExecutor擁有execute()和submit()提交異步任務的基礎功能，ScheduledThreadPoolExecutor類實現了ScheduledExecutorService，該接口定義了ScheduledThreadPoolExecutor能夠延時執行任務和周期執行任務的功能。

ScheduledThreadPoolExecutor也兩個重要的內部類：DelayedWorkQueue和ScheduledFutureTask。可以看出DelayedWorkQueue實現了BlockingQueue接口，也就是一個阻塞隊列，ScheduledFutureTask則是繼承了FutureTask類，也表示該類用于返回異步任務的結果。

/*** @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這里：

增加定時任務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));}}}

遍歷arrayList?

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跳出refresh

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Spring如何添加鉤子函數

這里沒有注冊鉤子函數自然是null

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

終于完了?

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觸發定時

倒著看就知道怎么調用的，實際上是反射執行上述方法的：

invoke方法用來在運行時動態地調用某個實例的方法

這里實行了Runnable 接口：?

反射，線程，線程池 底層還是這些技術！需要好好研究這塊代碼，加深理解基本原理。

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擴展信息：SpringBoot中定時任務默認是串行執行 如何設置并行

SpringBoot 使用@Scheduled注解配置串行、并行定時任務

Spring Boot 中實現定時任務的兩種方式

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