spring源码分析之定时任务Scheduled注解

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1. @Scheduled 可以将一个方法标识为可定时执行的。但必须指明cron()，fixedDelay(),或者fixedRate()属性。

注解的方法必须是无输入参数并返回空类型void的。

@Scheduled注解由注册的ScheduledAnnotationBeanPostProcessor来处理，该processor可以通过手动来注册，更方面的方式是通过<task:annotation-driven/>或者@EnableScheduling来注册。@EnableScheduling可以注册的原理是什么呢？先看定义：

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(SchedulingConfiguration.class)
@Documented
public @interface EnableScheduling {}

可以看到@EnableScheduling的实现由SchedulingConfiguration来完成。

@Configuration
public class SchedulingConfiguration { @Bean(name = AnnotationConfigUtils.SCHEDULED_ANNOTATION_PROCESSOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public ScheduledAnnotationBeanPostProcessor scheduledAnnotationProcessor() {
return new ScheduledAnnotationBeanPostProcessor();
}}

从上述代码可以看出，SchedulingConfiguration注册了一个ScheduledAnnotationBeanPostProcessor。

来看一下ScheduledAnnotationBeanPostProcessor来如何处理定时任务的？

protected void processScheduled(Scheduled scheduled, Method method, Object bean) {
try {
Assert.isTrue(void.class.equals(method.getReturnType()),
"Only void-returning methods may be annotated with @Scheduled");
Assert.isTrue(method.getParameterTypes().length == 0,
"Only no-arg methods may be annotated with @Scheduled"); if (AopUtils.isJdkDynamicProxy(bean)) {
try {
// Found a @Scheduled method on the target class for this JDK proxy ->
// is it also present on the proxy itself?
method = bean.getClass().getMethod(method.getName(), method.getParameterTypes());
}
catch (SecurityException ex) {
ReflectionUtils.handleReflectionException(ex);
}
catch (NoSuchMethodException ex) {
throw new IllegalStateException(String.format(
"@Scheduled method '%s' found on bean target class '%s' but not " +
"found in any interface(s) for a dynamic proxy. Either pull the " +
"method up to a declared interface or switch to subclass (CGLIB) " +
"proxies by setting proxy-target-class/proxyTargetClass to 'true'",
method.getName(), method.getDeclaringClass().getSimpleName()));
}
}
else if (AopUtils.isCglibProxy(bean)) {
// Common problem: private methods end up in the proxy instance, not getting delegated.
if (Modifier.isPrivate(method.getModifiers())) {
LogFactory.getLog(ScheduledAnnotationBeanPostProcessor.class).warn(String.format(
"@Scheduled method '%s' found on CGLIB proxy for target class '%s' but cannot " +
"be delegated to target bean. Switch its visibility to package or protected.",
method.getName(), method.getDeclaringClass().getSimpleName()));
}
} Runnable runnable = new ScheduledMethodRunnable(bean, method);
boolean processedSchedule = false;
String errorMessage =
"Exactly one of the 'cron', 'fixedDelay(String)', or 'fixedRate(String)' attributes is required"; // Determine initial delay
long initialDelay = scheduled.initialDelay();
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);
}
try {
initialDelay = Integer.parseInt(initialDelayString);
}
catch (NumberFormatException ex) {
throw new IllegalArgumentException(
"Invalid initialDelayString value \"" + initialDelayString + "\" - cannot parse into integer");
}
} // Check cron expression
String cron = scheduled.cron();
if (StringUtils.hasText(cron)) {
Assert.isTrue(initialDelay == -1, "'initialDelay' not supported for cron triggers");
processedSchedule = true;
String zone = scheduled.zone();
if (this.embeddedValueResolver != null) {
cron = this.embeddedValueResolver.resolveStringValue(cron);
zone = this.embeddedValueResolver.resolveStringValue(zone);
}
TimeZone timeZone;
if (StringUtils.hasText(zone)) {
timeZone = StringUtils.parseTimeZoneString(zone);
}
else {
timeZone = TimeZone.getDefault();
}
this.registrar.addCronTask(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 = scheduled.fixedDelay();
if (fixedDelay >= 0) {
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
this.registrar.addFixedDelayTask(new IntervalTask(runnable, fixedDelay, initialDelay));
}
String fixedDelayString = scheduled.fixedDelayString();
if (StringUtils.hasText(fixedDelayString)) {
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
if (this.embeddedValueResolver != null) {
fixedDelayString = this.embeddedValueResolver.resolveStringValue(fixedDelayString);
}
try {
fixedDelay = Integer.parseInt(fixedDelayString);
}
catch (NumberFormatException ex) {
throw new IllegalArgumentException(
"Invalid fixedDelayString value \"" + fixedDelayString + "\" - cannot parse into integer");
}
this.registrar.addFixedDelayTask(new IntervalTask(runnable, fixedDelay, initialDelay));
} // Check fixed rate
long fixedRate = scheduled.fixedRate();
if (fixedRate >= 0) {
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
this.registrar.addFixedRateTask(new IntervalTask(runnable, fixedRate, initialDelay));
}
String fixedRateString = scheduled.fixedRateString();
if (StringUtils.hasText(fixedRateString)) {
Assert.isTrue(!processedSchedule, errorMessage);
processedSchedule = true;
if (this.embeddedValueResolver != null) {
fixedRateString = this.embeddedValueResolver.resolveStringValue(fixedRateString);
}
try {
fixedRate = Integer.parseInt(fixedRateString);
}
catch (NumberFormatException ex) {
throw new IllegalArgumentException(
"Invalid fixedRateString value \"" + fixedRateString + "\" - cannot parse into integer");
}
this.registrar.addFixedRateTask(new IntervalTask(runnable, fixedRate, initialDelay));
} // Check whether we had any attribute set
Assert.isTrue(processedSchedule, errorMessage);
}
catch (IllegalArgumentException ex) {
throw new IllegalStateException(
"Encountered invalid @Scheduled method '" + method.getName() + "': " + ex.getMessage());
}
}

从上面的代码可以看出：@Scheduled有三个属性，分别是：

cron expression

fixedDelay

fixedRate

根据这些属性的不同，都加入到ScheduledTaskRegistrar来管理定时任务：

/**
* Schedule all registered tasks against the underlying {@linkplain
* #setTaskScheduler(TaskScheduler) task scheduler}.
*/
protected void scheduleTasks() {
long now = System.currentTimeMillis(); if (this.taskScheduler == null) {
this.localExecutor = Executors.newSingleThreadScheduledExecutor();
this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);
}
if (this.triggerTasks != null) {
for (TriggerTask task : this.triggerTasks) {
this.scheduledFutures.add(this.taskScheduler.schedule(
task.getRunnable(), task.getTrigger()));
}
}
if (this.cronTasks != null) {
for (CronTask task : this.cronTasks) {
this.scheduledFutures.add(this.taskScheduler.schedule(
task.getRunnable(), task.getTrigger()));
}
}
if (this.fixedRateTasks != null) {
for (IntervalTask task : this.fixedRateTasks) {
if (task.getInitialDelay() > 0) {
Date startTime = new Date(now + task.getInitialDelay());
this.scheduledFutures.add(this.taskScheduler.scheduleAtFixedRate(
task.getRunnable(), startTime, task.getInterval()));
}
else {
this.scheduledFutures.add(this.taskScheduler.scheduleAtFixedRate(
task.getRunnable(), task.getInterval()));
}
}
}
if (this.fixedDelayTasks != null) {
for (IntervalTask task : this.fixedDelayTasks) {
if (task.getInitialDelay() > 0) {
Date startTime = new Date(now + task.getInitialDelay());
this.scheduledFutures.add(this.taskScheduler.scheduleWithFixedDelay(
task.getRunnable(), startTime, task.getInterval()));
}
else {
this.scheduledFutures.add(this.taskScheduler.scheduleWithFixedDelay(
task.getRunnable(), task.getInterval()));
}
}
}
}