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 — 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：

​​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​​

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