如何仅显示文件更改事件 Java 的一条消息

Question

当文件结构更改时。我不断为更改的每个文件获得println s。如何使我在 10 秒内只能获得一个println进行多次更改？

try {
    WatchService watchService = FileSystems.getDefault().newWatchService();
    Path path = new File("C:\Users\myuser\Desktop\TestFolder").toPath();
    path.register(
        watchService,
        StandardWatchEventKinds.ENTRY_CREATE,
        StandardWatchEventKinds.ENTRY_DELETE,
        StandardWatchEventKinds.ENTRY_MODIFY);
    WatchKey key;
    while ((key = watchService.take()) != null) {
        for (WatchEvent<?> event : key.pollEvents()) {
            System.out.println(
                "Event kind:" + event.kind() + ". File affected: " + event.context() + ".");
            System.out.println("Something changed!");
            Thread.sleep(10000);
            System.out.println("Resuming..");
            break;
        }
        key.reset();
    }
} catch (IOException e) {
    e.printStackTrace();
} catch (InterruptedException e) {
    e.printStackTrace();
}

Answer 1

好吧，你可以做一些类似的事情，使用WatchService.poll(long timeout, TimeUnit unit)和Thread.sleep(10000)组合。

看看这个

   /**
     * Method used for tracking corresponding events( create,delete, modify )  
     * for a given directory every 10 seconds.
     * @throws InterruptedException 
     */
    private void monitoringWithTenSecondsLate() throws InterruptedException {
        WatchKey watchKey = null;
        while (true) {
            try {
                //poll everything every 10 seconds
                watchKey = watchService.poll(10, TimeUnit.SECONDS);
                for (WatchEvent<?> watchEvent : watchKey.pollEvents()) {
                    WatchEvent.Kind<?> kind = watchEvent.kind();
                    System.out.println("Event occured for " + watchEvent.context().toString() + " " + kind.toString());
                }
            } catch (InterruptedException ex) {
                Logger.getLogger(WatchServiceExample10SecondsLate.class.getName()).log(Level.SEVERE, null, ex);
            }
            //don't reset watch key for 10 seconds
            Thread.sleep(10000);
            boolean reset = watchKey.reset();
            if (!reset) {
                break;
            }
        }
    }

完整的代码可以从这里获得：Github代码的监视服务10秒示例。

Answer 2

我只是轮询所有键并连接结果。

大致如下：

while ((key = watchService.take()) != null) {
    StringJoiner joiner = new StringJoiner(",");
    for (WatchEvent<?> event : key.pollEvents()) {
        joiner.add(event.getContext().toString())        
    }
    key.reset();
    Thread.sleep(10000);
    System.out.println("Resuming ...");
    System.out.println("Something has changed! Affected files:" + joiner.toString())
}

Answer 3

所以现在，据我了解，线程休眠时的事件会被排队，仍然会被处理。我想你想要的，从你写的内容来看，仍然是处理这些事件，但只打印 10 秒后事件的总列表。在这种情况下，处理事件的 Thread.sleep(( 不是一个好的解决方案。

您可以做的是为观察程序实现一个线程，例如，以线程安全的方式将其注册的每个事件添加到变量中，以便您的主线程在 10 秒后访问。因此，在您的主线程中，您将有一个循环，该循环将休眠 10 秒，并在醒来时检索此变量，将其打印出来并重置它。

它会是这样的：

private Object lock = new Object(); // defined in your watcher class
private String events = new String() // also defined in your class
thread = new Thread(listeningFunc);
thread.start()
while(True) {
    Thread.sleep(10000);
    syncronized(lock) {
        System.out.println(events);
        events = new String()
    }
}
// With this function defined in your class to run in your new thread
listeningFunc() {
    path.register(
        watchService,
        StandardWatchEventKinds.ENTRY_CREATE,
        StandardWatchEventKinds.ENTRY_DELETE,
        StandardWatchEventKinds.ENTRY_MODIFY);
    WatchKey key;
    while((key = watchService.take()) != null) {
        for (WatchEvent<?> event : key.pollEvents()) {
            syncronized(lock) {
                events += "Event kind:" + event.kind() + ". File affected: " + event.context() + ".n"
            }
        }
        key.reset()
    }
}