SpringBoot定时任务 - Spring自带的定时任务是如何实现的？有何注意点？

通过前文我们基本梳理了定时任务体系：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，再到Quartz以及分布式任务（ElasticJob，xxl-job等等）。对于Springboot简单应用，还可以采用Spring自带task方式，本文主要介绍Spring自带的Task的案例和其实现方式。@pdai

实现案例

Spring Task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Spring Task实现方式。@pdai

使用Spring Task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。

Spring Task的原理？

Spring Task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