Spring调度任务 - 只运行一次 [英] Spring scheduling task - run only once

问题描述

是否可以在正好指定的时间只调度一次Spring服务方法？例如，当前时间是2pm，但是当我点击操作按钮，我想我的服务方法在晚上8点开始。我熟悉@Scheduled注释，我不知道如何写cron表达式不定期运行。这一个 @Scheduled（cron =0 0 20 * *？）每天晚上8点发射。

任何建议？

Is it possible to schedule Spring service method only once at exactly specified time? For example, current time is 2pm but when I hit the action button I want that my service method starts at 8pm. I'm familiar with @Scheduled annotation and I'm not sure how to write cron expression not to run periodically. This one @Scheduled(cron = "0 0 20 * * ?") fires every day at 8pm.
Any suggestions?

推荐答案

你可以使用Spring的TaskScheduler的实现。我在下面提供了一个不需要太多配置的示例（ConcurrentTaskScheduler，它包含单线程的预定执行器）。

You can use one of Spring's TaskScheduler's implementations. I provided an example below with one which does not require too much configuration (ConcurrentTaskScheduler that wraps a single-threaded scheduled executor).

方法是一个命名为 schedule 的方法，它只有一个Runnable
和Date。这将导致任务在
指定时间之后运行一次。所有其他方法都能够调度
任务重复运行。

The simplest method is the one named schedule that takes a Runnable and Date only. That will cause the task to run once after the specified time. All of the other methods are capable of scheduling tasks to run repeatedly.

阅读更多任务执行&计划

简单的工作范例：

private TaskScheduler scheduler;

Runnable exampleRunnable = new Runnable(){
    @Override
    public void run() {
        System.out.println("Works");
    }
};

@Async
public void executeTaskT() {
    ScheduledExecutorService localExecutor = Executors.newSingleThreadScheduledExecutor();
    scheduler = new ConcurrentTaskScheduler(localExecutor);

    scheduler.schedule(exampleRunnable,
            new Date(1432152000000L));//today at 8 pm UTC - replace it with any timestamp in miliseconds to text
}

...

executeTaskT() //call it somewhere after the spring application has been configured

请注意：

要启用对@Scheduled和@Async批注添加
@EnableScheduling和@EnableAsync到您的@Configuration
类之一

To enable support for @Scheduled and @Async annotations add @EnableScheduling and @EnableAsync to one of your @Configuration classes

---

更新 - 取消预定任务

---

Update - cancelling the scheduled task

TaskScheduler的计划方法返回ScheduledFuture，

TaskScheduler's schedule method returns a ScheduledFuture which is a delayed result-bearing action that can be cancelled.

因此，为了取消它，你需要保留计划任务的句柄（即保留ScheduledFuture返回对象）

So in order to cancel it, you need to keep a handle to the scheduled task (i.e. keep the ScheduledFuture return object).

更改上述取消任务的代码：

Changes to the code above for cancelling the task :

1. 在executeTaskT方法之外声明ScheduledFuture。
   
private ScheduledFuture scheduledFuture;


1. Declare the ScheduledFuture outside your executeTaskT method. private ScheduledFuture scheduledFuture;

修改您的通话以保持返回对象的原样：

scheduledFuture = scheduler.schedule（exampleRunnable，
new Date（1432152000000L））;


Modify your call to schedule to keep the return object as such: scheduledFuture = scheduler.schedule(exampleRunnable, new Date(1432152000000L));

在您的代码中某处的scheduledFuture对象上调用cancel

boolean mayInterruptIfRunning = true;
scheduledFuture.cancel（mayInterruptIfRunning）;


Call cancel on the scheduledFuture object somewhere in your code boolean mayInterruptIfRunning = true; scheduledFuture.cancel(mayInterruptIfRunning);

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