@Scheduled SpringBoot source code analysis of the

Springboot write notes @Scheduled regular tasks can be achieved,

Do a little analysis of its source code here

@Service
public class MyScheduled {

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

Configuration file 100 seconds

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

Important class 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

Find MyScheduled custom

Reverse seen here first to find the code, and then further on to find his assigned place

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));
				}

Important class ScheduledThreadPoolExecutor

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

ScheduledThreadPoolExecutor inherited ThreadPoolExecutor, that ScheduledThreadPoolExecutor have execute () and submit () submit basic functions of asynchronous tasks, ScheduledThreadPoolExecutor class implements ScheduledExecutorServicethis interface defines ScheduledThreadPoolExecutor can delay the implementation of tasks and functions to perform tasks cycle.

ScheduledThreadPoolExecutor also two important inner classes: DelayedWorkQueue and ScheduledFutureTask . It can be seen DelayedWorkQueue achieved BlockingQueue the interface, which is a blocking queue, ScheduledFutureTask is inherited FutureTask class, said class is used to return the results of asynchronous tasks.

/**
     * @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;
    }

To schedule here:

Increase regular tasks 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));
			}
		}
	}