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关于java:SpringBoot定时任务-Spring自带的定时任务是如何实现的有何注意点

jiezi

通过前文咱们根本梳理了定时工作体系：Timer 和 ScheduledExecutorService 是 JDK 内置的定时工作计划，以及 Netty 外部基于工夫轮实现的 HashedWheelTimer，再到 Quartz 以及分布式工作（ElasticJob，xxl-job 等等）。对于 Springboot 简略利用，还能够采纳 Spring 自带 task 形式，本文次要介绍 Spring 自带的 Task 的案例和其实现形式。@pdai

  • SpringBoot 定时工作 – Spring 自带的定时工作是如何实现的？有何留神点？

    • 实现案例

      • @EnableScheduling+@Scheduled

    • 进一步了解

      • 应用 Spring Task 要留神什么？

      • Spring Task 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 解决
    • 示例源码
    • 更多内容

实现案例

Spring Task 封装的比拟好，应用非常简单。

@EnableScheduling+@Scheduled

  • 通过 @EnableScheduling 启用定时工作，@Scheduled 定义工作
@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 所反对的参数：
  1. cron：cron 表达式，指定工作在特定工夫执行；
  2. fixedDelay：示意上一次工作执行实现后多久再次执行，参数类型为 long，单位 ms；
  3. fixedDelayString：与 fixedDelay 含意一样，只是参数类型变为 String；
  4. fixedRate：示意按肯定的频率执行工作，参数类型为 long，单位 ms；
  5. fixedRateString: 与 fixedRate 的含意一样，只是将参数类型变为 String；
  6. initialDelay：示意提早多久再第一次执行工作，参数类型为 long，单位 ms；
  7. initialDelayString：与 initialDelay 的含意一样，只是将参数类型变为 String；
  8. zone：时区，默认为以后时区，个别没有用到。

进一步了解

咱们再通过一些问题来帮忙你更深刻了解 Spring Task 实现形式。@pdai

应用 Spring Task 要留神什么？

  • 对于异样解决

倡议自行处理异样

  • 对于超时解决

在理论的开发中，这个问题常常会呈现，比方执行一段时间后定时工作不再执行了；这种状况会产生在，比方你调用一个第三方接口，没有设置调用超时，继而引发异样，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

增加 @EnableScheduling 注解会主动注入 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 配置中主动初始化 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? 咱们在前文中有详解的解说，具体看 Spring 外围之管制反转 (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 最次要的是注册各种类型的 task（这种形式在新的版本中曾经废除了）

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 注解是增加到办法级别，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 所反对的参数：

  1. cron：cron 表达式，指定工作在特定工夫执行；
  2. fixedDelay：示意上一次工作执行实现后多久再次执行，参数类型为 long，单位 ms；
  3. fixedDelayString：与 fixedDelay 含意一样，只是参数类型变为 String；
  4. fixedRate：示意按肯定的频率执行工作，参数类型为 long，单位 ms；
  5. fixedRateString: 与 fixedRate 的含意一样，只是将参数类型变为 String；
  6. initialDelay：示意提早多久再第一次执行工作，参数类型为 long，单位 ms；
  7. initialDelayString：与 initialDelay 的含意一样，只是将参数类型变为 String；
  8. zone：时区，默认为以后时区，个别没有用到。

获取到办法上 Scheduled 注解（对工作的定义），通过 processScheduled 解决具体类型的 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 解决

默认是 ConcurrentTaskScheduler，解决办法如下

@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 规范，它的解决办法如下

/**
    * 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;}
        });
    }
}

如果没有应用 EnterpriseConcurrentTriggerScheduler, 则应用 ReschedulingRunnable，实质上由 ScheduledExecutorService 解决

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/t…

更多内容

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