如何在Java中设置计时器?

How to set a Timer, say for 2 minutes, to try to connect to a Database then throw exception if there is any issue in connection?

如何设置一个计时器，比如2分钟，尝试连接到数据库，如果连接中有任何问题，抛出异常?

5 个解决方案

#1

230

So the first part of the answer is how to do what the subject asks as this was how I initially interpreted it and a few people seemed to find helpful. The question was since clarified and I've extended the answer to address that.

所以答案的第一部分是如何做题目问的，因为这是我最初的解释，一些人似乎觉得很有帮助。这个问题后来被澄清了，我扩展了答案来解决这个问题。

Setting a timer

设置一个计时器

First you need to create a Timer (I'm using the java.util version here):

首先需要创建一个计时器(我正在使用java)。util版本):

import java.util.Timer;

. .

Timer timer = new Timer();

To run the task once you would do:

要执行任务，你必须:

timer.schedule(new TimerTask() {
  @Override
  public void run() {
    // Your database code here
  }
}, 2*60*1000);

To have the task repeat after the duration you would do:

要让任务在持续时间后重复，你要做的是:

timer.scheduleAtFixedRate(new TimerTask() {
  @Override
  public void run() {
    // Your database code here
  }
}, 2*60*1000, 2*60*1000);

Making a task timeout

使一个任务超时

To specifically do what the clarified question asks, that is attempting to perform a task for a given period of time, you could do the following:

具体地做一下明确的问题，即试图在给定的时间内完成一项任务，你可以做到以下几点:

ExecutorService service = Executors.newSingleThreadExecutor();

try {
    Runnable r = new Runnable() {
        @Override
        public void run() {
            // Database task
        }
    };

    Future<?> f = service.submit(r);

    f.get(2, TimeUnit.MINUTES);     // attempt the task for two minutes
}
catch (final InterruptedException e) {
    // The thread was interrupted during sleep, wait or join
}
catch (final TimeoutException e) {
    // Took too long!
}
catch (final ExecutionException e) {
    // An exception from within the Runnable task
}
finally {
    service.shutdown();
}

This will execute normally with exceptions if the task completes within 2 minutes. If it runs longer than that, the TimeoutException will be throw.

如果任务在2分钟内完成，此操作将正常执行。如果运行的时间超过此时间，则抛出TimeoutException。

One issue is that although you'll get a TimeoutException after the two minutes, the task will actually continue to run, although presumably a database or network connection will eventually time out and throw an exception in the thread. But be aware it could consume resources until that happens.

一个问题是，尽管在两分钟后您将获得一个TimeoutException，但任务实际上将继续运行，尽管数据库或网络连接最终将超时并在线程中抛出异常。但要注意，在这种情况发生之前，它可能会消耗资源。

#2

Use this

使用这个

long startTime = System.currentTimeMillis();
long elapsedTime = 0L.

while (elapsedTime < 2*60*1000) {
    //perform db poll/check
    elapsedTime = (new Date()).getTime() - startTime;
}

//Throw your exception

#3

Ok, I think I understand your problem now. You can use a Future to try to do something and then timeout after a bit if nothing has happened.

好的，我想我现在明白你的问题了。你可以用未来来尝试做一些事情，如果什么事都没有发生，那么可以在一段时间后暂停。

E.g.:

例如:

FutureTask<Void> task = new FutureTask<Void>(new Callable<Void>() {
  @Override
  public Void call() throws Exception {
    // Do DB stuff
    return null;
  }
});

Executor executor = Executors.newSingleThreadScheduledExecutor();
executor.execute(task);

try {
  task.get(5, TimeUnit.SECONDS);
}
catch(Exception ex) {
  // Handle your exception
}

#4

How to stop the timer? Stop and play again when do something in this code

如何停止计时器?当在此代码中做一些事情时，停止并再次播放

timer.scheduleAtFixedRate(new TimerTask() {
  @Override
  public void run() {
    // Your database code here
  }
}, 2*60*1000, 2*60*1000);

When I use the timer.cancel();

当我使用timer。cancel();

it will stop but if close the form and open it again the exception is thrown

它将停止，但如果关闭表单并再次打开它，就会抛出异常。

Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: Timer already cancelled.
    at java.util.Timer.sched(Timer.java:354)
    at java.util.Timer.scheduleAtFixedRate(Timer.java:296)
    at View.Electronic_Meeting.this_componentShown(Electronic_Meeting.java:295)
    at View.Electronic_Meeting.access$000(Electronic_Meeting.java:36)
    at View.Electronic_Meeting$1.componentShown(Electronic_Meeting.java:85)
    at java.awt.AWTEventMulticaster.componentShown(AWTEventMulticaster.java:162)
    at java.awt.Component.processComponentEvent(Component.java:6095)
    at java.awt.Component.processEvent(Component.java:6043)
    at java.awt.Container.processEvent(Container.java:2041)
    at java.awt.Component.dispatchEventImpl(Component.java:4630)
    at java.awt.Container.dispatchEventImpl(Container.java:2099)
    at java.awt.Component.dispatchEvent(Component.java:4460)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

#5

    new java.util.Timer().schedule(new TimerTask(){
        @Override
        public void run() {
            System.out.println("Executed...");
           //your code here 
           //1000*5=5000 mlsec. i.e. 5 seconds. u can change accordngly 
        }
    },1000*5,1000*5);

#1

230