80

当我尝试注册文件而不是目录时java.nio.file.NotDirectoryException,会抛出异常。我可以监听单个文件更改,而不是整个目录吗?

4

7 回答 7

107

只需过滤目录中所需文件的事件:

final Path path = FileSystems.getDefault().getPath(System.getProperty("user.home"), "Desktop");
System.out.println(path);
try (final WatchService watchService = FileSystems.getDefault().newWatchService()) {
    final WatchKey watchKey = path.register(watchService, StandardWatchEventKinds.ENTRY_MODIFY);
    while (true) {
        final WatchKey wk = watchService.take();
        for (WatchEvent<?> event : wk.pollEvents()) {
            //we only register "ENTRY_MODIFY" so the context is always a Path.
            final Path changed = (Path) event.context();
            System.out.println(changed);
            if (changed.endsWith("myFile.txt")) {
                System.out.println("My file has changed");
            }
        }
        // reset the key
        boolean valid = wk.reset();
        if (!valid) {
            System.out.println("Key has been unregisterede");
        }
    }
}

在这里,我们检查更改的文件是否为“myFile.txt”,如果是,则执行任何操作。

于 2013-04-27T11:22:22.943 回答
21

其他答案是正确的,您必须查看目录并过滤特定文件。但是,您可能希望在后台运行一个线程。接受的答案可以无限期地阻止watchService.take();并且不会关闭 WatchService。适用于单独线程的解决方案可能如下所示:

public class FileWatcher extends Thread {
    private final File file;
    private AtomicBoolean stop = new AtomicBoolean(false);

    public FileWatcher(File file) {
        this.file = file;
    }

    public boolean isStopped() { return stop.get(); }
    public void stopThread() { stop.set(true); }

    public void doOnChange() {
        // Do whatever action you want here
    }

    @Override
    public void run() {
        try (WatchService watcher = FileSystems.getDefault().newWatchService()) {
            Path path = file.toPath().getParent();
            path.register(watcher, StandardWatchEventKinds.ENTRY_MODIFY);
            while (!isStopped()) {
                WatchKey key;
                try { key = watcher.poll(25, TimeUnit.MILLISECONDS); }
                catch (InterruptedException e) { return; }
                if (key == null) { Thread.yield(); continue; }

                for (WatchEvent<?> event : key.pollEvents()) {
                    WatchEvent.Kind<?> kind = event.kind();

                    @SuppressWarnings("unchecked")
                    WatchEvent<Path> ev = (WatchEvent<Path>) event;
                    Path filename = ev.context();

                    if (kind == StandardWatchEventKinds.OVERFLOW) {
                        Thread.yield();
                        continue;
                    } else if (kind == java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY
                            && filename.toString().equals(file.getName())) {
                        doOnChange();
                    }
                    boolean valid = key.reset();
                    if (!valid) { break; }
                }
                Thread.yield();
            }
        } catch (Throwable e) {
            // Log or rethrow the error
        }
    }
}

我尝试从接受的答案和这篇文章开始工作。您应该能够使用该线程new FileWatcher(new File("/home/me/myfile")).start()并通过调用该线程来停止它stopThread()

于 2015-01-02T03:30:35.067 回答
21

不,不可能注册文件,监视服务不能以这种方式工作。但是注册一个目录实际上会观察子目录(文件和子目录)的变化,而不是目录本身的变化。

如果要监视文件,则向监视服务注册包含目录。Path.register() 文档说:

WatchKey java.nio.file.Path.register(WatchService watcher, Kind[] events, Modifier... modifiers) 抛出 IOException

将此路径中的文件注册到监视服务。

在此版本中,此路径定位一个存在的目录。该目录已注册到监视服务,以便可以监视目录中的条目

然后您需要处理条目上的事件,并通过检查事件的上下文值来检测与您感兴趣的文件相关的事件。上下文值表示条目的名称(实际上是条目相对于其父路径的路径,也就是子名称)。你有一个例子在这里

于 2014-06-25T06:27:32.017 回答
10

Apache 提供了一个带有方法的FileWatchDog类。doOnChange

private class SomeWatchFile extends FileWatchdog {

    protected SomeWatchFile(String filename) {
        super(filename);
    }

    @Override
    protected void doOnChange() {
        fileChanged= true;
    }

}

你可以在任何地方开始这个线程:

SomeWatchFile someWatchFile = new SomeWatchFile (path);
someWatchFile.start();

FileWatchDog 类轮询文件的lastModified()时间戳。Java NIO 的原生 WatchService 更高效,因为通知是即时的。

于 2014-02-17T09:57:24.267 回答
8

您不能直接观看单个文件,但可以过滤掉不需要的文件。

这是我的FileWatcher类实现:

import java.io.File;
import java.nio.file.*;
import java.nio.file.WatchEvent.Kind;

import static java.nio.file.StandardWatchEventKinds.*;

public abstract class FileWatcher
{
    private Path folderPath;
    private String watchFile;

    public FileWatcher(String watchFile)
    {
        Path filePath = Paths.get(watchFile);

        boolean isRegularFile = Files.isRegularFile(filePath);

        if (!isRegularFile)
        {
            // Do not allow this to be a folder since we want to watch files
            throw new IllegalArgumentException(watchFile + " is not a regular file");
        }

        // This is always a folder
        folderPath = filePath.getParent();

        // Keep this relative to the watched folder
        this.watchFile = watchFile.replace(folderPath.toString() + File.separator, "");
    }

    public void watchFile() throws Exception
    {
        // We obtain the file system of the Path
        FileSystem fileSystem = folderPath.getFileSystem();

        // We create the new WatchService using the try-with-resources block
        try (WatchService service = fileSystem.newWatchService())
        {
            // We watch for modification events
            folderPath.register(service, ENTRY_MODIFY);

            // Start the infinite polling loop
            while (true)
            {
                // Wait for the next event
                WatchKey watchKey = service.take();

                for (WatchEvent<?> watchEvent : watchKey.pollEvents())
                {
                    // Get the type of the event
                    Kind<?> kind = watchEvent.kind();

                    if (kind == ENTRY_MODIFY)
                    {
                        Path watchEventPath = (Path) watchEvent.context();

                        // Call this if the right file is involved
                        if (watchEventPath.toString().equals(watchFile))
                        {
                            onModified();
                        }
                    }
                }

                if (!watchKey.reset())
                {
                    // Exit if no longer valid
                    break;
                }
            }
        }
    }

    public abstract void onModified();
}

要使用它,您只需onModified()像这样扩展和实现该方法:

import java.io.File;

public class MyFileWatcher extends FileWatcher
{
    public MyFileWatcher(String watchFile)
    {
        super(watchFile);
    }

    @Override
    public void onModified()
    {
        System.out.println("Modified!");
    }
}

最后,开始看文件:

String watchFile = System.getProperty("user.home") + File.separator + "Desktop" + File.separator + "Test.txt";
FileWatcher fileWatcher = new MyFileWatcher(watchFile);
fileWatcher.watchFile();
于 2016-10-12T16:24:35.490 回答
5

不确定其他人,但我抱怨使用基本 WatchService API 监视单个文件以进行更改所需的代码量。它必须更简单!

以下是使用第三方库的几个替代方案:

于 2015-04-30T12:17:48.007 回答
5

我围绕 Java 1.7 创建了一个包装器WatchService,它允许注册一个目录和任意数量的glob模式。此类将负责过滤并仅发出您感兴趣的事件。

try {
    DirectoryWatchService watchService = new SimpleDirectoryWatchService(); // May throw
    watchService.register( // May throw
            new DirectoryWatchService.OnFileChangeListener() {
                @Override
                public void onFileCreate(String filePath) {
                    // File created
                }

                @Override
                public void onFileModify(String filePath) {
                    // File modified
                }

                @Override
                public void onFileDelete(String filePath) {
                    // File deleted
                }
            },
            <directory>, // Directory to watch
            <file-glob-pattern-1>, // E.g. "*.log"
            <file-glob-pattern-2>, // E.g. "input-?.txt"
            <file-glob-pattern-3>, // E.g. "config.ini"
            ... // As many patterns as you like
    );

    watchService.start(); // The actual watcher runs on a new thread
} catch (IOException e) {
    LOGGER.error("Unable to register file change listener for " + fileName);
}

完整的代码在这个repo中。

于 2015-06-23T14:07:20.787 回答