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?
7 回答
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。
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()
。
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。
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。
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();
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:
- 使用 Apache Commons 配置
- 使用 Spring Framework 中的 spring-loaded 包(没有找到这个副手的示例实现,但它看起来很容易使用)
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。