ScheduledExecutorService只运行一次

Question

我希望一个进程在我启动我的网络服务后运行，然后每隔30分钟左右运行一次（我现在用较小的延迟测试它，只是为了看看它是否工作），但是我的进程从来不会运行超过一次。我做错了什么？

这是我的密码：

@WebListener
public class SchedulerService implements ServletContextListener{

    @Autowired
    UpdateSubscriberService updateSubscriberService;

    ScheduledExecutorService scheduledExecService;

    public SchedulerService(){
        scheduledExecService = Executors.newSingleThreadScheduledExecutor();
    }

    @Override
    public void contextDestroyed(ServletContextEvent arg0) {
        scheduledExecService.shutdown();
    }

    @Override
    public void contextInitialized(ServletContextEvent arg0) {
        scheduledExecService.scheduleWithFixedDelay(new Runnable(){
            @Override
            public void run() {
                Date date = new Date(System.currentTimeMillis());
                System.out.println("Running scheduled update check " + date.toString());
                updateSubscriberService.checkForUpdates();
            }
        }, 60, 30, TimeUnit.SECONDS);
    }
}

Answer 1

如果您遇到这样的情况：即使最后一次运行尚未完成，代码也必须每隔这么多秒运行一次（如果管理不当，可能会非常危险），您可以在计时器内的不同线程中启动进程。下面是示例代码。

ScheduledExecutorService scheduledExecService = newSingleThreadScheduledExecutor();
scheduledExecService.scheduleWithFixedDelay(new Runnable()
{
    @Override
    public void run()
    {
        // This should be in a try-catch because any error here
        // will stop the recurrence
        try
        {
            // The timer will only repeat if the last run is finished. So
            // we put each new process in a different thread than the timer
            // itself, so the last timer call "finishes" as soon as the process
            // leaves the timer's thread.
            Thread t = new Thread(new Runnable()
            {
                public void run()
                {
                    try
                    {
                        android.os.Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
                        MyProcessThatShouldRunEverySoManySecondsNoMatterWhat();
                    }
                    catch (Exception erTimerThread)
                    {
                        Log.e("Error", erTimerThread.toString());
                    }
                }
            });
            t.setPriority(2);
            t.start();
        }
        catch (Exception erTimer)
        {
            Log.e("Error", erTimer.toString());
        }
    }
}, 0, 60, java.util.concurrent.TimeUnit.SECONDS);

Answer 2

请看我对一个类似问题的回答。

只是猜测一下：正在抛出异常。ScheduledExecutorService如果遇到异常，将静默停止，不再执行进一步的计划工作。

run方法的代码应该始终由try-catch包围，以处理和吸收任何抛出的异常。

 @Override
 public void run() {
    try {  // Let no Exception reach the ScheduledExecutorService.
        Date date = new Date(System.currentTimeMillis());
        System.out.println("Running scheduled update check " + date.toString());
        updateSubscriberService.checkForUpdates();
    } catch ( Exception e ) {
        System.out.println( "ERROR - unexpected exception" );
    }
}

慢慢来。从一个run方法开始，该方法只执行系统。出来println。