java - 观察者在改变后停止

Question

如何将下面的 Watcher 转换为持续运行？我希望它即使在检测到更改后也能继续侦听文件。也许是一个线程？

import java.io.IOException;
import java.nio.file.*;
import java.util.List;

public class Listener {

    public static void main(String[] args) {

        Path myDir = Paths.get("C:/file_dir/listen_to_this");

        try {
            WatchService watcher = myDir.getFileSystem().newWatchService();
            myDir.register(watcher, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE, StandardWatchEventKinds.ENTRY_MODIFY);
            WatchKey watckKey = watcher.take();
            List<WatchEvent<?>> events = watckKey.pollEvents();
            for (WatchEvent event : events) {
                if (event.kind() == StandardWatchEventKinds.ENTRY_CREATE) {
                    System.out.println("Created: " + event.context().toString());
                }
                if (event.kind() == StandardWatchEventKinds.ENTRY_DELETE) {
                    System.out.println("Delete: " + event.context().toString());
                }
                if (event.kind() == StandardWatchEventKinds.ENTRY_MODIFY) {
                    System.out.println("Modify: " + event.context().toString());
                }
            }
        } catch (IOException | InterruptedException e) {
            System.out.println("Error: " + e.toString());
        }
    }
}

Answer 1

不再需要任何线程。你可以简单地把它放在一个while循环中：

public static void main(String[] args) throws Exception {
    Path myDir = Paths.get("C:/file_dir/listen_to_this");

    WatchService watcher = myDir.getFileSystem().newWatchService();
    myDir.register(watcher, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE, StandardWatchEventKinds.ENTRY_MODIFY);

    while (true) {
        WatchKey watckKey = watcher.take();
        List<WatchEvent<?>> events = watckKey.pollEvents();
        for (WatchEvent event : events) {
            if (event.kind() == StandardWatchEventKinds.ENTRY_CREATE) {
                System.out.println("Created: " + event.context().toString());
            }
            if (event.kind() == StandardWatchEventKinds.ENTRY_DELETE) {
                System.out.println("Delete: " + event.context().toString());
            }
            if (event.kind() == StandardWatchEventKinds.ENTRY_MODIFY) {
                System.out.println("Modify: " + event.context().toString());
            }
        }
        watchKey.reset();
    }
}