使用ThreadPoolTaskExecutor在特定日期调用方法

Question

我有一个方法希望使用Spring运行一次，它需要在给定的java.util上运行。日期（或LocalDateTime）。我计划将该方法应该执行的所有日期持久化到数据源。它应该异步运行。

一种方法是每天检查数据库中的日期，如果日期已过且尚未执行，则执行该方法。有没有更好的方法？

我知道Spring提供了ThreadPoolTaskScheduler和ThreadPool TaskExecutor。我正在查看TaskScheduler界面中的ScheduledFuture计划（可运行任务，日期开始时间）。我需要创建RunnableSpring托管bean来调用我的方法吗？或者有更简单的注释可以做到这一点吗？举个例子真的很有帮助。

（也看了这里。）

Answer 1

查看@Scheduled注释。它可能会实现你想要的。

@Scheduled(cron="*/5 * * * * MON-FRI")
public void scheduledDateWork() {
    Date date = new Date(); //or use DAO call to look up date in database

    executeLogic(date);
}

克朗表达的例子来自另一个答案:

"0 0 * * * *" = the top of every hour of every day.
"*/10 * * * * *" = every ten seconds.
"0 0 8-10 * * *" = 8, 9 and 10 o'clock of every day.
"0 0/30 8-10 * * *" = 8:00, 8:30, 9:00, 9:30 and 10 o'clock every day.
"0 0 9-17 * * MON-FRI" = on the hour nine-to-five weekdays
"0 0 0 25 12 ?" = every Christmas Day at midnight

Answer 2

通过将计划日期外部化(到数据库)，典型的计划实践(即基于cron的或固定的计划)不再适用。给定目标日期，您可以按如下方式准确地计划任务:

Date now = new Date();
Date next = ... get next date from external source ...
long delay = next.getTime() - now.getTime();
scheduler.schedule(Runnable task, delay, TimeUnit.MILLISECONDS);

剩下的就是创建一种有效的方法来调度每个新任务。下面有一个 TaskDispatcher 线程，它根据下一个 java.util.Date（您从数据库中读取）来调度每个任务。无需每天检查;此方法足够灵活，可以与存储在数据库中的任何计划方案一起使用。

接下来是说明该方法的工作代码。

使用的示例任务；在这种情况下，只是Hibernate一段固定的时间。当任务完成时，TaskDispatcher会通过Count下拉锁发出信号。

public class Task implements Runnable {

    private final CountDownLatch completion;
    public Task(CountDownLatch completion) {
        this.completion = completion;
    }

    @Override
    public void run() {
        System.out.println("Doing task");
        try {
            Thread.sleep(60*1000);  // Simulate the job taking 60 seconds
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        completion.countDown();     // Signal that the job is complete
    }

}

调度程序负责读取下一个计划日期的数据库，启动可运行的 ScheduledFuture 并等待任务完成。

public class TaskDispatcher implements Runnable {

    private static final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);
    private boolean isInterrupted = false;

    @Override
    public void run() {

        while (!isInterrupted) {

            Date now = new Date();

            System.out.println("Reading database for next date");
            Date next = ... read next data from database ...

            //Date next = new Date();   // Used as test
            //next.setTime(now.getTime()+10*1000); // Used as test

            long delay = next.getTime() - now.getTime();
            System.out.println("Scheduling next task with delay="+delay);

            CountDownLatch latch = new CountDownLatch(1);
            ScheduledFuture<?> countdown = scheduler.schedule(new Task(latch), delay, TimeUnit.MILLISECONDS);

            try {
                System.out.println("Blocking until the current job has completed");
                latch.await();
            } catch (InterruptedException e) {
                System.out.println("Thread has been requested to stop");
                isInterrupted = true;
            }
            if (!isInterrupted)
                System.out.println("Job has completed normally");
        }

        scheduler.shutdown();

    }

}

TaskDispatcher 的启动方式如下（使用 Spring Boot） - 像通常使用 Spring 一样启动线程：

@Bean
public TaskExecutor taskExecutor() {
    return new SimpleAsyncTaskExecutor(); // Or use another one of your liking
}

@Bean
public CommandLineRunner schedulingRunner(TaskExecutor executor) {
    return new CommandLineRunner() {
        public void run(String... args) throws Exception {
            executor.execute(new TaskDispatcher());
        }
    };
}

让我知道这种方法是否适用于您的用例。