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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

@Servicepublic 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

@Nullable	private BeanFactory beanFactory;

private void finishRegistration() {		if (this.scheduler != null) {			this.registrar.setScheduler(this.scheduler);		}		if (this.beanFactory instanceof ListableBeanFactory) {			Map
   
     beans =					((ListableBeanFactory) this.beanFactory).getBeansOfType(SchedulingConfigurer.class);			List
    
      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：

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
   
    (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

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。

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