ScheduledExecutorService只运行一次

Question

我希望在启动我的网络服务之后运行一个进程，然后每隔30分钟左右运行一次（我现在以较小的延迟测试它，只是为了查看它是否有效），但是我的进程永远不会跑一次。我做错了什么？

这是我的代码：

@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

使用run

包裹try catch代码

只是一个猜测：抛出异常。如果遇到异常，ScheduledExecutorService会静默停止。

run方法的代码应始终被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" );
    }
}

删除run方法

采取婴儿步骤。从run方法开始，除了System.out.println之外什么都不做。

Answer 2

即使在最后一次运行尚未完成的情况下，即使代码始终每隔几秒运行一次（如果管理不当，这很危险），您也可以启动您的进程位于计时器内的其他线程中。这是示例代码。

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);