如何在 Java 中设置计时器? [英] How to set a Timer in Java?
问题描述
如何设置一个计时器,比如 2 分钟,尝试连接到数据库然后在连接有任何问题时抛出异常?
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?
推荐答案
所以答案的第一部分是如何做主题要求的事情,因为这是我最初的解释方式,而且似乎有一些人觉得有帮助.这个问题后来得到了澄清,我已经扩展了答案来解决这个问题.
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.
设置计时器
首先你需要创建一个 Timer(我在这里使用的是 java.util
版本):
First you need to create a Timer (I'm using the java.util
version here):
import java.util.Timer;
...
Timer timer = new Timer();
一旦你想运行任务:
timer.schedule(new TimerTask() {
@Override
public void run() {
// Your database code here
}
}, 2*60*1000);
// Since Java-8
timer.schedule(() -> /* your database code here */, 2*60*1000);
要在您将执行的持续时间之后重复任务:
To have the task repeat after the duration you would do:
timer.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
// Your database code here
}
}, 2*60*1000, 2*60*1000);
// Since Java-8
timer.scheduleAtFixedRate(() -> /* your database code here */, 2*60*1000, 2*60*1000);
使任务超时
要具体执行澄清问题所要求的操作,即尝试在给定时间段内执行任务,您可以执行以下操作:
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:
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();
}
如果任务在 2 分钟内完成,这将正常执行,但有异常.如果它运行的时间超过这个时间,就会抛出 TimeoutException.
This will execute normally with exceptions if the task completes within 2 minutes. If it runs longer than that, the TimeoutException will be throw.
一个问题是,虽然你会在两分钟后得到一个 TimeoutException,任务实际上会继续运行,尽管据推测数据库或网络连接最终会超时并抛出异常线程.但请注意,在此之前它可能会消耗资源.
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.
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