Insight spring @Scheduled 解析过程

接着上一篇<task:annotation-driven>解析，Insight @Scheduled 解析。

1、@Scheduled注解方法的加载

// bean 初始化后触发callback，ScheduledAnnotationBeanPostProcessor完成@Scheduled 的处理
// 参考InitializingBean's afterPropertiesSet
public Object postProcessAfterInitialization(final Object bean, String beanName) {
// ...
ReflectionUtils.doWithMethods(targetClass, new MethodCallback() {
public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
Scheduled scheduled = AnnotationUtils.getAnnotation(method, Scheduled.class);
if (scheduled != null) {
processScheduled(scheduled, method, bean);
annotatedMethods.add(method);
}
}
});
// ...
return bean;
}

2、@Scheduled注解方法的处理

根据Scheduled属性构造不同类型的Task（triggerTasks、cronTasks、fixedRateTasks、fixedDelayTasks），然后注册到ScheduledTaskRegistrar，最后由其激活Task。

3、激活Task

registrar.afterPropertiesSet();

public class ScheduledTaskRegistrar implements InitializingBean, DisposableBean {

public void afterPropertiesSet() {
scheduleTasks();
}

/**
* Schedule all registered tasks against the underlying task scheduler.
*/
protected void scheduleTasks() {
long now = System.currentTimeMillis();

if (this.taskScheduler == null) {
// Executors 熟悉吧，JDK自带的并发框架来了。
this.localExecutor = Executors.newSingleThreadScheduledExecutor();
// Executor包装类，实现不同类型task的分发实现，如下述的CronTask
this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);
}
// ...
if (this.cronTasks != null) {
// cron 表达式类型的Task处理
for (CronTask task : this.cronTasks) {
// 构造ReschedulingRunnable(task, trigger)真正实现task 调度
this.scheduledFutures.add(this.taskScheduler.schedule(task.getRunnable(), task.getTrigger()));
}
}
// ...
}
}// ReschedulingRunnable见名知义，reuse-schedule
class ReschedulingRunnable extends DelegatingErrorHandlingRunnable implements ScheduledFuture

4、finally，调度任务就乖乖的定时execute啦。

附ScheduledExecutorService自带Example：

// ScheduledExecutorService Usage Example
static class BeeperControl {
private final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

public void beepForAnHour() {
final Runnable beeper = new Runnable() {
public void run() {
System.out.println("beep");
}
};
// beep every ten seconds
final ScheduledFuture<?> beeperHandle = scheduler.scheduleAtFixedRate(beeper, 10, 10, TimeUnit.SECONDS);
// after an hour cancel execution of task
scheduler.schedule(new Runnable() {
public void run() {
beeperHandle.cancel(true);
}
}, 60 * 60, TimeUnit.SECONDS);
}
}