spring schedule任务调度方式

public Object postProcessAfterInitialization(Object bean, String beanName) {
		if (bean instanceof AopInfrastructureBean || bean instanceof TaskScheduler ||
				bean instanceof ScheduledExecutorService) {
			// Ignore AOP infrastructure such as scoped proxies.
			return bean;
		}
		//解析所有的@Scheduled注解
		Class<?> targetClass = AopProxyUtils.ultimateTargetClass(bean);
		if (!this.nonAnnotatedClasses.contains(targetClass) &&
				AnnotationUtils.isCandidateClass(targetClass, Arrays.asList(Scheduled.class, Schedules.class))) {
			Map<Method, Set<Scheduled>> annotatedMethods = MethodIntrospector.selectMethods(targetClass,
					(MethodIntrospector.MetadataLookup<Set<Scheduled>>) method -> {
						Set<Scheduled> scheduledAnnotations = AnnotatedElementUtils.getMergedRepeatableAnnotations(
								method, Scheduled.class, Schedules.class);
						return (!scheduledAnnotations.isEmpty() ? scheduledAnnotations : null);
					});
			if (annotatedMethods.isEmpty()) {
				this.nonAnnotatedClasses.add(targetClass);
							}
			else {
				// 调用processScheduled（）方法初始化调度任务
				annotatedMethods.forEach((method, scheduledAnnotations) ->
						scheduledAnnotations.forEach(scheduled -> processScheduled(scheduled, method, bean)));
				
			}
		}
		return bean;
	}

processScheduled(Scheduled scheduled, Method method, Object bean)

protected Runnable createRunnable(Object target, Method method) {
  //@Scheduled 注解修饰的方法必须是无参的
		Assert.isTrue(method.getParameterCount() == 0, "Only no-arg methods may be annotated with @Scheduled");
		Method invocableMethod = AopUtils.selectInvocableMethod(method, target.getClass());
		return new ScheduledMethodRunnable(target, invocableMethod);
	}

ReflectionUtils.makeAccessible(this.method);
this.method.invoke(this.target);

this.registrar.scheduleCronTask()
this.registrar.scheduleFixedDelayTask()
this.registrar.scheduleFixedRateTask()

public ScheduledTask scheduleCronTask(CronTask task) {
		ScheduledTask scheduledTask = this.unresolvedTasks.remove(task);
		boolean newTask = false;
		if (scheduledTask == null) {
			scheduledTask = new ScheduledTask(task);
			newTask = true;
		}
  //taskScheduler是否初始化
		if (this.taskScheduler != null) {
          //创建任务
			scheduledTask.future = this.taskScheduler.schedule(task.getRunnable(), task.getTrigger());
		}
		else {//taskScheduler未初始化，将任务放到未处理列表里
			addCronTask(task);
			this.unresolvedTasks.put(task, scheduledTask);
		}
		return (newTask ? scheduledTask : null);
	}

/**
runnable就是封装的ScheduledMethodRunnable
*/
this.registrar.scheduleCronTask(new CronTask(runnable, new CronTrigger(cron /**cron表达式*/, timeZone)))

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) {
				
				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) {
				
				// Search for ScheduledExecutorService bean next...
				try {
					this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, false));
				}
				catch (NoUniqueBeanDefinitionException ex2) {
					
					try {
						this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, true));
					}
					catch (NoSuchBeanDefinitionException ex3) {
						
					}
				}
				catch (NoSuchBeanDefinitionException ex2) {
					
					// Giving up -> falling back to default scheduler within the registrar...
					logger.info("No TaskScheduler/ScheduledExecutorService bean found for scheduled processing");
				}
			}
		}

		this.registrar.afterPropertiesSet();
	}

	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));
			}
		}
	}

public ScheduledFuture<?> schedule(Runnable task, Trigger trigger) {
		try {
			if (this.enterpriseConcurrentScheduler) {
				return new EnterpriseConcurrentTriggerScheduler().schedule(decorateTask(task, true), trigger);
			}
			else {
				ErrorHandler errorHandler =
						(this.errorHandler != null ? this.errorHandler : TaskUtils.getDefaultErrorHandler(true));
				return new ReschedulingRunnable(task, trigger, this.clock, this.scheduledExecutor, errorHandler).schedule();
			}
		}
		catch (RejectedExecutionException ex) {
			throw new TaskRejectedException("Executor [" + this.scheduledExecutor + "] did not accept task: " + task, ex);
		}
	}

public ScheduledFuture<?> schedule() {
		synchronized (this.triggerContextMonitor) {
			this.scheduledExecutionTime = this.trigger.nextExecutionTime(this.triggerContext);
			if (this.scheduledExecutionTime == null) {
				return null;
			}
			long initialDelay = this.scheduledExecutionTime.getTime() - this.triggerContext.getClock().millis();
			this.currentFuture = this.executor.schedule(this, initialDelay, TimeUnit.MILLISECONDS);
			return this;
		}
	}

public void run() {
		Date actualExecutionTime = new Date(this.triggerContext.getClock().millis());
		super.run();
		Date completionTime = new Date(this.triggerContext.getClock().millis());
		synchronized (this.triggerContextMonitor) {
			Assert.state(this.scheduledExecutionTime != null, "No scheduled execution");
			this.triggerContext.update(this.scheduledExecutionTime, actualExecutionTime, completionTime);
			if (!obtainCurrentFuture().isCancelled()) {
				schedule();
			}
		}
	}

public DelegatingErrorHandlingRunnable(Runnable delegate, ErrorHandler errorHandler) {
		Assert.notNull(delegate, "Delegate must not be null");
		Assert.notNull(errorHandler, "ErrorHandler must not be null");
		this.delegate = delegate;
		this.errorHandler = errorHandler;
	}
public void run() {
		try {
			this.delegate.run();
		}
		catch (UndeclaredThrowableException ex) {
			this.errorHandler.handleError(ex.getUndeclaredThrowable());
		}
		catch (Throwable ex) {
			this.errorHandler.handleError(ex);
		}
	}