Java:WatchService:File.Lastmodified 返回 0

Question

我正在尝试编写一个基本的目录监视器，用于打印文件是否已创建、更改或删除。但是我无法显示每个文件的“lastModified”时间。请参阅下面的完整代码:

public static void main(String[] args) throws IOException, InterruptedException {
    // TODO Auto-generated method stub

    WatchService watcher = FileSystems.getDefault().newWatchService();

    Path dir = Paths.get("C:\\Users\\User1\\Desktop\\test");

    WatchKey key = dir.register(watcher,

            StandardWatchEventKinds.ENTRY_CREATE,
            StandardWatchEventKinds.ENTRY_DELETE,
            StandardWatchEventKinds.ENTRY_MODIFY
            );

    for (;;) {


        WatchKey key2 = watcher.take(); 

        for ( WatchEvent<?> event : key.pollEvents()  ) {

            WatchEvent.Kind<?> kind = event.kind();


            WatchEvent<Path> ev = (WatchEvent<Path>) event; 

            Path filename = ev.context(); 
            File fullFilename = filename.toFile();

            System.out.println("Event: |"+kind+"| Filename: "+fullFilename.getName()+"|Time: "+fullFilename.lastModified());


            if (fullFilename.exists()) {


                System.out.println(fullFilename.getName()+" - Exists");

            }

            else {

                System.out.println("fullFileName does not exist");

            }

        }


        boolean valid = key.reset();
        if (!valid) {
            break;
        }
    }


}

lastModified 方法返回 0。我曾尝试测试 fileFullname 对象是否实际存在，但由于某种原因它不存在。然而，当您使用 fileFullname.getName() 时，它会很好地返回文件名。

我做错了什么？

非常感谢您的帮助，在此先感谢您!

Answer 1

您需要根据监视的目录解析文件名。

您无法获取 lastModified 值，因为事件的上下文文件系统没有将您监视的目录作为 defaultDirectory，defaultDirectory 是应用程序运行的目录，如果您检查 fullFilename 是否存在，您将得到 false

Path filename = ev.context(); 
File fullFilename = filename.toFile();
//fullFilename.exists(); returns false

所以你需要这样解决

Path name = (Path) event.context();
//dir is you watched directory
File filename = dir.resolve(name).toFile();

完整代码

import java.io.File;
import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardWatchEventKinds;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;

public class Snippet {
    public static void main(String[] args) throws IOException, InterruptedException {

        Path pathToWatch = FileSystems.getDefault().getPath("C:\\tmp\\test");
        try (WatchService watchService = pathToWatch.getFileSystem().newWatchService()) {
            Path dir = Paths.get("C:\\tmp\\test");
            dir.register(watchService, StandardWatchEventKinds.ENTRY_MODIFY, StandardWatchEventKinds.ENTRY_CREATE, StandardWatchEventKinds.ENTRY_DELETE);
            WatchKey key = watchService.take();
            do {
                for (final WatchEvent<?> event : key.pollEvents()) {
                    Path name = (Path) event.context();
                    File filename = dir.resolve(name).toFile();
                    System.out.println(dir + ": " + event.kind() + ": " + event.context() + ", Modified: " + filename.lastModified());
                }
            } while (key.reset());
        }
    }
}

更多信息请访问 docs.oracle.com (Watching a Directory for Changes)

希望对你有帮助