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 @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

@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

/ * 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

/ * 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

// 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:

@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)); } } 

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:

@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:

@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:

@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:

@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:

@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