SpringBoot定时任务 - Spring Schedule实现方式

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SpringBoot定时任务 - Spring Schedule实现方式

前文我们介绍了Timer和ScheduledExecutorService是JDK内置的定时任务方案以及Netty内部基于时间轮实现的HashedWheelTimer；而主流的SpringBoot集成方案有两种，一种是Spring Sechedule, 另一种是Spring集成Quartz；本文主要介绍Spring Schedule实现方式。@pdai

SpringBoot定时任务 - Spring Schedule实现方式
准备知识点
什么是cron表达式
实现案例
@EnableScheduling+@Scheduled
进一步理解
使用Spring Schedule要注意什么？
SpringTask的原理？
@EnableScheduling注解
SchedulingConfiguration中初始化ScheduledAnnotationBeanPostProcessor
ScheduledTaskRegistrar注册task
ScheduledAnnotationBeanPostProcessor加载Scheduled注解
ScheduledTaskRegistrar 中解析task
TaskScheduler对Task处理
示例源码

准备知识点

cron表达式，以及BeanPostProcessor（方便你理解它的原理，相关介绍在之前的文章中Spring核心之控制反转(IOC)源码解析）.

什么是cron表达式

定时任务和CRON表达式在开发中使用也非常广泛；在学习时，总体上理解，对常用的知悉，开发时可以快速查询使用即可。 相关文章

CRON表达式 - CRON表达式介绍和使用
定时任务和CRON表达式在开发中使用也非常广泛，本文整理了CRON表达式和常见使用例子
CRON表达式 - CRON生成和校验工具
本文主要总结常用的在线CRON生成和校验工具，从而高效的写出正确的表达式

实现案例

SpringTask封装的比较好，使用非常简单。

@EnableScheduling+@Scheduled

通过@EnableScheduling启用定时任务，@Scheduled定义任务

    @EnableScheduling
    @Configuration
    public class ScheduleDemo {

        /** * 每隔1分钟执行一次。 */
        @Scheduled(fixedRate = 1000 * 60 * 1)
        public void runScheduleFixedRate() {
            log.info("runScheduleFixedRate: current DateTime, {}", LocalDateTime.now());
        }

        /** * 每个整点小时执行一次。 */
        @Scheduled(cron = "0 0 */1 * * ?")
        public void runScheduleCron() {
            log.info("runScheduleCron: current DateTime, {}", LocalDateTime.now());
        }

    }

@Scheduled所支持的参数：
cron：cron表达式，指定任务在特定时间执行；
fixedDelay：表示上一次任务执行完成后多久再次执行，参数类型为long，单位ms；
fixedDelayString：与fixedDelay含义一样，只是参数类型变为String；
fixedRate：表示按一定的频率执行任务，参数类型为long，单位ms；
fixedRateString: 与fixedRate的含义一样，只是将参数类型变为String；
initialDelay：表示延迟多久再第一次执行任务，参数类型为long，单位ms；
initialDelayString：与initialDelay的含义一样，只是将参数类型变为String；
zone：时区，默认为当前时区，一般没有用到。

进一步理解

我们再通过一些问题来帮助你更深入理解SpringTask实现方式。@pdai

使用Spring Schedule要注意什么？

关于异常处理

建议自行处理异常

关于超时处理

在实际的开发中，这个问题经常会出现，比如执行一段时间后定时任务不再执行了；这种情况会发生在，比如你调用一个第三方接口，没有设置调用超时，继而引发异常，这时候当前任务便阻塞了。

SpringTask的原理？

SpringTask的源码在这里：

@EnableScheduling注解

添加@EnableScheduling注解会自动注入SchedulingConfiguration

     * @author Chris Beams
     * @author Juergen Hoeller
     * @since 3.1
     * @see Scheduled
     * @see SchedulingConfiguration
     * @see SchedulingConfigurer
     * @see ScheduledTaskRegistrar
     * @see Trigger
     * @see ScheduledAnnotationBeanPostProcessor
     */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Import(SchedulingConfiguration.class)
    @Documented
    public @interface EnableScheduling {

    }

SchedulingConfiguration中初始化ScheduledAnnotationBeanPostProcessor

SchedulingConfiguration配置中自动初始化ScheduledAnnotationBeanPostProcessor

    @Configuration(proxyBeanMethods = false)
    @Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    public class SchedulingConfiguration {

    	@Bean(name = TaskManagementConfigUtils.SCHEDULED_ANNOTATION_PROCESSOR_BEAN_NAME)
    	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
    	public ScheduledAnnotationBeanPostProcessor scheduledAnnotationProcessor() {
    		return new ScheduledAnnotationBeanPostProcessor();
    	}

    }

什么是BeanPostProcessor? 我们在前文中有详解的讲解，具体看Spring核心之控制反转(IOC)源码解析

Spring 容器中 Bean 的生命周期流程

ScheduledTaskRegistrar注册task

在ScheduledAnnotationBeanPostProcessor构造函数中初始化了ScheduledTaskRegistrar

    /** * Create a default {@code ScheduledAnnotationBeanPostProcessor}. */
    public ScheduledAnnotationBeanPostProcessor() {
        this.registrar = new ScheduledTaskRegistrar();
    }

ScheduledTaskRegistrar最主要的是注册各种类型的task （这种方式在新的版本中已经废弃了）

    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));
            }
        }
    }

注册哪些Task，怎么设计类的呢？

ScheduledAnnotationBeanPostProcessor加载Scheduled注解

在BeanPostProcessor的postProcessAfterInitialization阶段加载Scheduled注解

    @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> scheduledAnnotations = AnnotatedElementUtils.getMergedRepeatableAnnotations(
                                method, Scheduled.class, Schedules.class);
                        return (!scheduledAnnotations.isEmpty() ? scheduledAnnotations : 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, scheduledAnnotations) ->
                        scheduledAnnotations.forEach(scheduled -> processScheduled(scheduled, method, bean)));
                if (logger.isTraceEnabled()) {
                    logger.trace(annotatedMethods.size() + " @Scheduled methods processed on bean '" + beanName +
                            "': " + annotatedMethods);
                }
            }
        }
        return bean;
    }

Scheduled注解是添加到方法级别，具体如下

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

    	/** * A special cron expression value that indicates a disabled trigger: {@value}. * <p>This is primarily meant for use with <code>${...}</code> placeholders, * allowing for external disabling of corresponding scheduled methods. * @since 5.1 * @see ScheduledTaskRegistrar#CRON_DISABLED */
    	String CRON_DISABLED = ScheduledTaskRegistrar.CRON_DISABLED;


    	/** * A cron-like expression, extending the usual UN*X definition to include triggers * on the second, minute, hour, day of month, month, and day of week. * <p>For example, {@code "0 * * * * MON-FRI"} means once per minute on weekdays * (at the top of the minute - the 0th second). * <p>The fields read from left to right are interpreted as follows. * <ul> * <li>second</li> * <li>minute</li> * <li>hour</li> * <li>day of month</li> * <li>month</li> * <li>day of week</li> * </ul> * <p>The special value {@link #CRON_DISABLED "-"} indicates a disabled cron * trigger, primarily meant for externally specified values resolved by a * <code>${...}</code> placeholder. * @return an expression that can be parsed to a cron schedule * @see org.springframework.scheduling.support.CronExpression#parse(String) */
    	String cron() default "";

    	/** * A time zone for which the cron expression will be resolved. By default, this * attribute is the empty String (i.e. the server's local time zone will be used). * @return a zone id accepted by {@link java.util.TimeZone#getTimeZone(String)}, * or an empty String to indicate the server's default time zone * @since 4.0 * @see org.springframework.scheduling.support.CronTrigger#CronTrigger(String, java.util.TimeZone) * @see java.util.TimeZone */
    	String zone() default "";

    	/** * Execute the annotated method with a fixed period between the end of the * last invocation and the start of the next. * <p>The time unit is milliseconds by default but can be overridden via * {@link #timeUnit}. * @return the delay */
    	long fixedDelay() default -1;

    	/** * Execute the annotated method with a fixed period between the end of the * last invocation and the start of the next. * <p>The time unit is milliseconds by default but can be overridden via * {@link #timeUnit}. * @return the delay as a String value &mdash; for example, a placeholder * or a {@link java.time.Duration#parse java.time.Duration} compliant value * @since 3.2.2 */
    	String fixedDelayString() default "";

    	/** * Execute the annotated method with a fixed period between invocations. * <p>The time unit is milliseconds by default but can be overridden via * {@link #timeUnit}. * @return the period */
    	long fixedRate() default -1;

    	/** * Execute the annotated method with a fixed period between invocations. * <p>The time unit is milliseconds by default but can be overridden via * {@link #timeUnit}. * @return the period as a String value &mdash; for example, a placeholder * or a {@link java.time.Duration#parse java.time.Duration} compliant value * @since 3.2.2 */
    	String fixedRateString() default "";

    	/** * Number of units of time to delay before the first execution of a * {@link #fixedRate} or {@link #fixedDelay} task. * <p>The time unit is milliseconds by default but can be overridden via * {@link #timeUnit}. * @return the initial * @since 3.2 */
    	long initialDelay() default -1;

    	/** * Number of units of time to delay before the first execution of a * {@link #fixedRate} or {@link #fixedDelay} task. * <p>The time unit is milliseconds by default but can be overridden via * {@link #timeUnit}. * @return the initial delay as a String value &mdash; for example, a placeholder * or a {@link java.time.Duration#parse java.time.Duration} compliant value * @since 3.2.2 */
    	String initialDelayString() default "";

    	/** * The {@link TimeUnit} to use for {@link #fixedDelay}, {@link #fixedDelayString}, * {@link #fixedRate}, {@link #fixedRateString}, {@link #initialDelay}, and * {@link #initialDelayString}. * <p>Defaults to {@link TimeUnit#MICROSECONDS}. * <p>This attribute is ignored for {@linkplain #cron() cron expressions} * and for {@link java.time.Duration} values supplied via {@link #fixedDelayString}, * {@link #fixedRateString}, or {@link #initialDelayString}. * @return the {@code TimeUnit} to use * @since 5.3.10 */
    	TimeUnit timeUnit() default TimeUnit.MILLISECONDS;

    }

@Scheduled所支持的参数：

cron：cron表达式，指定任务在特定时间执行；
fixedDelay：表示上一次任务执行完成后多久再次执行，参数类型为long，单位ms；
fixedDelayString：与fixedDelay含义一样，只是参数类型变为String；
fixedRate：表示按一定的频率执行任务，参数类型为long，单位ms；
fixedRateString: 与fixedRate的含义一样，只是将参数类型变为String；
initialDelay：表示延迟多久再第一次执行任务，参数类型为long，单位ms；
initialDelayString：与initialDelay的含义一样，只是将参数类型变为String；
zone：时区，默认为当前时区，一般没有用到。

获取到方法上Scheduled注解（对任务的定义），通过processScheduled处理具体类型的task

    /** * Process the given {@code @Scheduled} method declaration on the given bean. * @param scheduled the {@code @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 = convertToMillis(scheduled.initialDelay(), scheduled.timeUnit());
            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 = convertToMillis(initialDelayString, scheduled.timeUnit());
                    }
                    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 = convertToMillis(scheduled.fixedDelay(), scheduled.timeUnit());
            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 = convertToMillis(fixedDelayString, scheduled.timeUnit());
                    }
                    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 = convertToMillis(scheduled.fixedRate(), scheduled.timeUnit());
            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 = convertToMillis(fixedRateString, scheduled.timeUnit());
                    }
                    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());
        }
    }

ScheduledTaskRegistrar 中解析task

以CronTask为例，如果定义了taskScheduler则由taskScheduler执行，如果没有放到unresolvedTasks中。

    /** * Schedule the specified cron task, either right away if possible * or on initialization of the scheduler. * @return a handle to the scheduled task, allowing to cancel it * (or {@code null} if processing a previously registered task) * @since 4.3 */
    @Nullable
    public ScheduledTask scheduleCronTask(CronTask task) {
        ScheduledTask scheduledTask = this.unresolvedTasks.remove(task);
        boolean newTask = false;
        if (scheduledTask == null) {
            scheduledTask = new ScheduledTask(task);
            newTask = true;
        }
        if (this.taskScheduler != null) {
            scheduledTask.future = this.taskScheduler.schedule(task.getRunnable(), task.getTrigger());
        }
        else {
            addCronTask(task);
            this.unresolvedTasks.put(task, scheduledTask);
        }
        return (newTask ? scheduledTask : null);
    }

TaskScheduler对Task处理

默认是ConcurrentTaskScheduler，处理方法如下

    @Override
    @Nullable
    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);
        }
    }

EnterpriseConcurrentTriggerScheduler 是 JSR-236 Trigger标准，它的处理方法如下

    /** * Delegate that adapts a Spring Trigger to a JSR-236 Trigger. * Separated into an inner class in order to avoid a hard dependency on the JSR-236 API. */
    private class EnterpriseConcurrentTriggerScheduler {

        public ScheduledFuture<?> schedule(Runnable task, final Trigger trigger) {
            ManagedScheduledExecutorService executor = (ManagedScheduledExecutorService) scheduledExecutor;
            return executor.schedule(task, new javax.enterprise.concurrent.Trigger() {
                @Override
                @Nullable
                public Date getNextRunTime(@Nullable LastExecution le, Date taskScheduledTime) {
                    return (trigger.nextExecutionTime(le != null ?
                            new SimpleTriggerContext(le.getScheduledStart(), le.getRunStart(), le.getRunEnd()) :
                            new SimpleTriggerContext()));
                }
                @Override
                public boolean skipRun(LastExecution lastExecution, Date scheduledRunTime) {
                    return false;
                }
            });
        }
    }

如果没有使用EnterpriseConcurrentTriggerScheduler, 则使用ReschedulingRunnable，本质上由ScheduledExecutorService处理

    public ReschedulingRunnable(Runnable delegate, Trigger trigger, Clock clock,
    			ScheduledExecutorService executor, ErrorHandler errorHandler) {

        super(delegate, errorHandler);
        this.trigger = trigger;
        this.triggerContext = new SimpleTriggerContext(clock);
        this.executor = executor;
    }


    @Nullable
    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;
        }
    }

示例源码

https://github.com/realpdai/tech-pdai-spring-demos

SpringBoot定时任务 - Spring Schedule实现方式

# SpringBoot定时任务 - Spring Schedule实现方式

# 准备知识点

# 什么是cron表达式

# 实现案例

# @EnableScheduling+@Scheduled

# 进一步理解

# 使用Spring Schedule要注意什么？

# SpringTask的原理？

# @EnableScheduling注解

# SchedulingConfiguration中初始化ScheduledAnnotationBeanPostProcessor

# ScheduledTaskRegistrar注册task

# ScheduledAnnotationBeanPostProcessor加载Scheduled注解

# ScheduledTaskRegistrar 中解析task

# TaskScheduler对Task处理

# 示例源码

SpringBoot定时任务 - Spring Schedule实现方式

准备知识点

什么是cron表达式

实现案例

@EnableScheduling+@Scheduled

进一步理解

使用Spring Schedule要注意什么？

SpringTask的原理？

@EnableScheduling注解

SchedulingConfiguration中初始化ScheduledAnnotationBeanPostProcessor

ScheduledTaskRegistrar注册task

ScheduledAnnotationBeanPostProcessor加载Scheduled注解

ScheduledTaskRegistrar 中解析task

TaskScheduler对Task处理

示例源码