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

Posted 2022-08-06 realpdai

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：

1. ​​cron​​：cron表达式，指定任务在特定时间执行；
2. ​​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；
3. ​​fixedDelayString​​：与fixedDelay含义一样，只是参数类型变为String；
4. ​​fixedRate​​：表示按一定的频率执行任务，参数类型为long，单位ms；
5. ​​fixedRateString​​: 与fixedRate的含义一样，只是将参数类型变为String；
6. ​​initialDelay​​：表示延迟多久再第一次执行任务，参数类型为long，单位ms；
7. ​​initialDelayString​​：与initialDelay的含义一样，只是将参数类型变为String；
8. ​​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 servers 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 servers 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 — 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 — 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 — 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：

1. ​​cron​​：cron表达式，指定任务在特定时间执行；
2. ​​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；
3. ​​fixedDelayString​​：与fixedDelay含义一样，只是参数类型变为String；
4. ​​fixedRate​​：表示按一定的频率执行任务，参数类型为long，单位ms；
5. ​​fixedRateString​​: 与fixedRate的含义一样，只是将参数类型变为String；
6. ​​initialDelay​​：表示延迟多久再第一次执行任务，参数类型为long，单位ms；
7. ​​initialDelayString​​：与initialDelay的含义一样，只是将参数类型变为String；
8. ​​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 dont 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​​

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