SpringBoot定时任务@Scheduled注解详解

SpringBoot定时任务@Scheduled注解详解

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

@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Repeatable(Schedules.class)public @interfaceScheduled{

	Stringcron()default"";

	Stringzone()default"";longfixedDelay()default-1;

	StringfixedDelayString()default"";longfixedRate()default-1;

	StringfixedRateString()default"";longinitialDelay()default-1;

	StringinitialDelayString()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

@Overridepublic ObjectpostProcessAfterInitialization(Object bean, String beanName){if(beaninstanceofAopInfrastructureBean|| beaninstanceofTaskScheduler||
			beaninstanceofScheduledExecutorService){// 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

/**
 * 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)
 */protectedvoidprocessScheduled(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=newLinkedHashSet<>(4);// Determine initial delaylong 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){thrownewIllegalArgumentException("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(newCronTask(runnable,newCronTrigger(cron, timeZone))));}}}// At this point we don't need to differentiate between initial delay set or not anymoreif(initialDelay<0){
			initialDelay=0;}// Check fixed delaylong fixedDelay= scheduled.fixedDelay();if(fixedDelay>=0){
			Assert.isTrue(!processedSchedule, errorMessage);
			processedSchedule=true;
			tasks.add(this.registrar.scheduleFixedDelayTask(newFixedDelayTask(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){thrownewIllegalArgumentException("Invalid fixedDelayString value \""+ fixedDelayString+"\" - cannot parse into long");}
				tasks.add(this.registrar.scheduleFixedDelayTask(newFixedDelayTask(runnable, fixedDelay, initialDelay)));}}// Check fixed ratelong fixedRate= scheduled.fixedRate();if(fixedRate>=0){
			Assert.isTrue(!processedSchedule, errorMessage);
			processedSchedule=true;
			tasks.add(this.registrar.scheduleFixedRateTask(newFixedRateTask(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){thrownewIllegalArgumentException("Invalid fixedRateString value \""+ fixedRateString+"\" - cannot parse into long");}
				tasks.add(this.registrar.scheduleFixedRateTask(newFixedRateTask(runnable, fixedRate, initialDelay)));}}// Check whether we had any attribute set
		Assert.isTrue(processedSchedule, errorMessage);// Finally register the scheduled taskssynchronized(this.scheduledTasks){
			Set<ScheduledTask> regTasks=this.scheduledTasks.computeIfAbsent(bean, key->newLinkedHashSet<>(4));
			regTasks.addAll(tasks);}}catch(IllegalArgumentException ex){thrownewIllegalStateException("Encountered invalid @Scheduled method '"+ method.getName()+"': "+ ex.getMessage());}}

• org.springframework.scheduling.config.ScheduledTaskRegistrar#scheduleTasks

/**
 * Schedule all registered tasks against the underlying
 * {@linkplain #setTaskScheduler(TaskScheduler) task scheduler}.
 */
proectedvoidscheduleTasks(){if(this.taskScheduler== null){this.localExecutor= Executors.newSingleThreadScheduledExecutor();this.taskScheduler=newConcurrentTaskScheduler(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:

// org.springframework.scheduling.config.ScheduledTaskRegistrar#scheduleTasksif(this.taskScheduler== null){this.localExecutor= Executors.newSingleThreadScheduledExecutor();this.taskScheduler=newConcurrentTaskScheduler(this.localExecutor);}// java.util.concurrent.Executors#newSingleThreadScheduledExecutor()publicstatic ScheduledExecutorServicenewSingleThreadScheduledExecutor(){returnnewDelegatedScheduledExecutorService(newScheduledThreadPoolExecutor(1));}

代码示例:

@Slf4j@ComponentpublicclassRunIntervalTestScheduler{@Scheduled(cron="0/1 * * * * ?")publicvoidsingleThreadTest1(){
        log.info("singleThreadTest1");
        LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1));}@Scheduled(cron="0/1 * * * * ?")publicvoidsingleThreadTest2(){
        log.info("singleThreadTest2");
        LockSupport.parkNanos(TimeUnit.SECONDS.toNanos(1));}@Scheduled(cron="0/1 * * * * ?")publicvoidsingleThreadTest3(){
        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:

@ConfigurationpublicclassScheduledConfigimplementsSchedulingConfigurer{/**
     * 任务执行线程池大小
     */privatestaticfinalint TASK_POOL_SIZE=50;/**
     * 线程名
     */privatestaticfinal String TASK_THREAD_PREFIX="test-task-";@OverridepublicvoidconfigureTasks(ScheduledTaskRegistrar scheduledTaskRegistrar){
        ThreadPoolTaskScheduler taskPool=newThreadPoolTaskScheduler();
        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:

@Slf4j@ComponentpublicclassRunIntervalTestScheduler{@Scheduled(initialDelay=1000, fixedRate=1000)publicvoidfixedRate()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:

@Slf4j@ComponentpublicclassRunIntervalTestScheduler{@Scheduled(initialDelay=1000, fixedDelay=1000)publicvoidfixedDelay()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:

@Slf4j@ComponentpublicclassRunIntervalTestScheduler{@Scheduled(cron="0/1 * * * * ?")publicvoidcronRun()throws Exception{
        log.info("cron run");
        TimeUnit.SECONDS.sleep(3);}}