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

@Nullable
	private 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