目录

• 概述
• 注解定义
• 参数说明
• 源码解析
• 使用详解
• 定时任务同步/异步执行
• fixedRate/fixedDelay区别

项目开发中，经常会遇到定时任务的场景，Spring提供了@Scheduled注解，方便进行定时任务的开发

概述

要使用@Scheduled注解，首先需要在启动类添加@EnableScheduling，启用Spring的计划任务执行功能，这样可以在容器中的任何Spring管理的bean上检测@Scheduled注解，执行计划任务

注解定义

复制
@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(Schedules.class)
public @interface Scheduled {
 
	String cron() default "";
 
	String zone() default "";
 
	long fixedDelay() default -1;
 
	String fixedDelayString() default "";
 
	long fixedRate() default -1;
 
	String fixedRateString() default "";
	
	long initialDelay() default -1;
 
	String initialDelayString() default "";
}

参数说明

源码解析

配置了@Scheduled注解的方法，Spring的处理是通过注册ScheduledAnnotationBeanPostProcessor来执行，将不同配置参数的任务分配给不同的handler处理，核心代码如下

org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor#postProcessAfterInitialization

复制
@Override
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;
	}
 
	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> scheduledMethods = AnnotatedElementUtils.getMergedRepeatableAnnotations(
							method, Scheduled.class, Schedules.class);
					return (!scheduledMethods.isEmpty() ? scheduledMethods : null);
				});
		if (annotatedMethods.isEmpty()) {
			this.nonAnnotatedClasses.add(targetClass);
			if (logger.isTraceEnabled()) {
				logger.trace("No @Scheduled annotations found on bean class: " + targetClass);
			}
		}
		else {
			// Non-empty set of methods
			annotatedMethods.forEach((method, scheduledMethods) ->
					scheduledMethods.forEach(scheduled -> processScheduled(scheduled, method, bean)));
			if (logger.isTraceEnabled()) {
				logger.trace(annotatedMethods.size() + " @Scheduled methods processed on bean '" + beanName +
						"': " + annotatedMethods);
			}
		}
	}
	return bean;
}

org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor#processScheduled

复制
/**
 * Process the given {@code @Scheduled} method declaration on the given bean.
 * @param scheduled the @Scheduled annotation
 * @param method the method that the annotation has been declared on
 * @param bean the target bean instance
 * @see #createRunnable(Object, Method)
 */
protected void processScheduled(Scheduled scheduled, Method method, Object bean) {
	try {
		Runnable runnable = createRunnable(bean, method);
		boolean processedSchedule = false;
		String errorMessage =
				"Exactly one of the 'cron', 'fixedDelay(String)', or 'fixedRate(String)' attributes is required";
		Set<ScheduledTask> tasks = new LinkedHashSet<>(4);
		// Determine initial delay
		long initialDelay = scheduled.initialDelay();
		String initialDelayString = scheduled.initialDelayString();
		if (StringUtils.hasText(initialDelayString)) {
			Assert.isTrue(initialDelay < 0, "Specify 'initialDelay' or 'initialDelayString', not both");
			if (this.embeddedValueResolver != null) {
				initialDelayString = this.embeddedValueResolver.resolveStringValue(initialDelayString);
			}
			if (StringUtils.hasLength(initialDelayString)) {
				try {
					initialDelay = parseDelayAsLong(initialDelayString);
				}
				catch (RuntimeException ex) {
					throw new IllegalArgumentException(
							"Invalid initialDelayString value \"" + initialDelayString + "\" - cannot parse into long");
				}
			}
		}
		// Check cron expression
		String cron = scheduled.cron();
		if (StringUtils.hasText(cron)) {
			String zone = scheduled.zone();
			if (this.embeddedValueResolver != null) {
				cron = this.embeddedValueResolver.resolveStringValue(cron);
				zone = this.embeddedValueResolver.resolveStringValue(zone);
			}
			if (StringUtils.hasLength(cron)) {
				Assert.isTrue(initialDelay == -1, "'initialDelay' not supported for cron triggers");
				processedSchedule = true;
				if (!Scheduled.CRON_DISABLED.equals(cron)) {
					TimeZone timeZone;
					if (StringUtils.hasText(zone)) {
						timeZone = StringUtils.parseTimeZoneString(zone);
					}
					else {
						timeZone = TimeZone.getDefault();
					}
					tasks.add(this.registrar.scheduleCronTask(new CronTask(runnable, new CronTrigger(cron, timeZone))));
				}
			}
		}
		// At this point we don't need to differentiate between initial delay set or not anymore
		if (initialDelay < 0) {
			initialDelay = 0;
		}
		// Check fixed delay
		long fixedDelay = scheduled.fixedDelay();
		if (fixedDelay >= 0) {
			Assert.isTrue(!processedSchedule, errorMessage);
			processedSchedule = true;
			tasks.add(this.registrar.scheduleFixedDelayTask(new FixedDelayTask(runnable, fixedDelay, initialDelay)));
		}
		String fixedDelayString = scheduled.fixedDelayString();
		if (StringUtils.hasText(fixedDelayString)) {
			if (this.embeddedValueResolver != null) {
				fixedDelayString = this.embeddedValueResolver.resolveStringValue(fixedDelayString);
			}
			if (StringUtils.hasLength(fixedDelayString)) {
				Assert.isTrue(!processedSchedule, errorMessage);
				processedSchedule = true;
				try {
					fixedDelay = parseDelayAsLong(fixedDelayString);
				}
				catch (RuntimeException ex) {
					throw new IllegalArgumentException(
							"Invalid fixedDelayString value \"" + fixedDelayString + "\" - cannot parse into long");
				}
				tasks.add(this.registrar.scheduleFixedDelayTask(new FixedDelayTask(runnable, fixedDelay, initialDelay)));
			}
		}
		// Check fixed rate
		long fixedRate = scheduled.fixedRate();
		if (fixedRate >= 0) {
			Assert.isTrue(!processedSchedule, errorMessage);
			processedSchedule = true;
			tasks.add(this.registrar.scheduleFixedRateTask(new FixedRateTask(runnable, fixedRate, initialDelay)));
		}
		String fixedRateString = scheduled.fixedRateString();
		if (StringUtils.hasText(fixedRateString)) {
			if (this.embeddedValueResolver != null) {
				fixedRateString = this.embeddedValueResolver.resolveStringValue(fixedRateString);
			}
			if (StringUtils.hasLength(fixedRateString)) {
				Assert.isTrue(!processedSchedule, errorMessage);
				processedSchedule = true;
				try {
					fixedRate = parseDelayAsLong(fixedRateString);
				}
				catch (RuntimeException ex) {
					throw new IllegalArgumentException(
							"Invalid fixedRateString value \"" + fixedRateString + "\" - cannot parse into long");
				}
				tasks.add(this.registrar.scheduleFixedRateTask(new FixedRateTask(runnable, fixedRate, initialDelay)));
			}
		}
		// Check whether we had any attribute set
		Assert.isTrue(processedSchedule, errorMessage);
		// Finally register the scheduled tasks
		synchronized (this.scheduledTasks) {
			Set<ScheduledTask> regTasks = this.scheduledTasks.computeIfAbsent(bean, key -> new LinkedHashSet<>(4));
			regTasks.addAll(tasks);
		}
	}
	catch (IllegalArgumentException ex) {
		throw new IllegalStateException(
				"Encountered invalid @Scheduled method '" + method.getName() + "': " + ex.getMessage());
	}
}

org.springframework.scheduling.config.ScheduledTaskRegistrar#scheduleTasks

复制
/**
 * Schedule all registered tasks against the underlying
 * {@linkplain #setTaskScheduler(TaskScheduler) task scheduler}.
 */
proected 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));
		}
	}
}

使用详解

定时任务同步/异步执行

定时任务执行默认是单线程模式，会创建一个本地线程池，线程池大小为1。当项目中有多个定时任务时，任务之间会相互等待，同步执行

源码:

复制
// org.springframework.scheduling.config.ScheduledTaskRegistrar#scheduleTasks
if (this.taskScheduler == null) {
    this.localExecutor = Executors.newSingleThreadScheduledExecutor();
    this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);
}
 
// java.util.concurrent.Executors#newSingleThreadScheduledExecutor()
public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
    return new DelegatedScheduledExecutorService
        (new ScheduledThreadPoolExecutor(1));
}

代码示例:

复制
@Slf4j
@Component
public class RunIntervalTestScheduler {
 
    @Scheduled(cron = "0/1 * * * * ?")
    public void singleThreadTest1() {
        log.info("singleThreadTest1");
        LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1));
    }
 
    @Scheduled(cron = "0/1 * * * * ?")
    public void singleThreadTest2() {
        log.info("singleThreadTest2");
        LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1));
    }
 
    @Scheduled(cron = "0/1 * * * * ?")
    public void singleThreadTest3() {
        log.info("singleThreadTest3");
        LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1));
    }
}

执行结果:

可以看到，默认情况下，三个任务串行执行，都使用pool-1-thread-1同一个线程池，并且线程只有一个

可以通过实现SchedulingConfigurer接口，手动创建线程池，配置期望的线程数量

示例代码:

复制
@Configuration
public class ScheduledConfig implements SchedulingConfigurer {
 
    /**
     * 任务执行线程池大小
     */
    private static final int TASK_POOL_SIZE = 50;
    /**
     * 线程名
     */
    private static final String TASK_THREAD_PREFIX = "test-task-";
 
    @Override
    public void configureTasks(ScheduledTaskRegistrar scheduledTaskRegistrar) {
        ThreadPoolTaskScheduler taskPool = new ThreadPoolTaskScheduler();
        taskPool.setPoolSize(TASK_POOL_SIZE);
        taskPool.setThreadNamePrefix(TASK_THREAD_PREFIX);
        taskPool.initialize();
        scheduledTaskRegistrar.setTaskScheduler(taskPool);
    }
}

任务执行结果:

此时任务的执行已经异步化，从自定义线程池中分配线程执行任务，在实际应用中需要考虑实际任务数量，创建相应大小的线程池

fixedRate/fixedDelay区别

fixedRate是配置上一次任务执行开始到下一次执行开始的间隔时间，不会等待上一次任务执行完成就会调度下一次任务，将其放入等待队列中

代码示例:

复制
@Slf4j
@Component
public class RunIntervalTestScheduler {
 
    @Scheduled(initialDelay = 1000, fixedRate = 1000)
    public void fixedRate() throws Exception {
        log.info("fixedRate run");
        TimeUnit.SECONDS.sleep(3);
    }
}

执行结果:

任务配置的fixedRate为1s，执行日志打印的时间间隔都是3s左右，也就是上一次执行完成后，紧接着就执行下一次任务

fixedDelay是配置的上一次任务执行结束到下一次执行开始的间隔时间，也就是说会等待上一次任务执行结束后，延迟间隔时间，再执行下一次任务

代码示例:

复制
@Slf4j
@Component
public class RunIntervalTestScheduler {
 
    @Scheduled(initialDelay = 1000, fixedDelay = 1000)
    public void fixedDelay() throws Exception {
        log.info("fixedDelay run");
        TimeUnit.SECONDS.sleep(3);
    }
}

执行结果:

任务配置的fixedDelay为1s，执行日志打印的时间间隔都是4s左右，也就是上一次执行完成后，延迟1s后执行下一次任务

cron表达式如果配置为类似每秒执行、每分钟执行(例:0/1 * * * * ?, 每秒执行)，调度跟fixedDelay是一致的，也是在上一次任务执行结束后，等待间隔时间

代码示例:

复制
@Slf4j
@Component
public class RunIntervalTestScheduler {
 
    @Scheduled(cron = "0/1 * * * * ?")
    public void cronRun() throws Exception{
        log.info("cron run");
        TimeUnit.SECONDS.sleep(3);
    }
}

执行结果:

执行日志打印的时间间隔都是4s左右，也就是上一次执行完成后，延迟1s后执行下一次任务

cron表达式如果配置为固定时间执行(例:1 * * * * ?, 秒数为1时执行)，若上一次任务没有执行完，则不会调度本次任务，跳过本次执行，等待下一次执行周期

代码示例:

复制
@Slf4j
@Component
public class RunIntervalTestScheduler {
 
    @Scheduled(cron = "1 * * * * ?")
    public void cronRun() throws Exception{
        log.info("cron run");
        TimeUnit.SECONDS.sleep(70);
    }
}

执行结果:

上一次任务未执行完毕，则跳过了本次执行