当我尝试注册文件而不是目录时java.nio.file.NotDirectoryException。我可以听一个文件更改，而不听整个目录吗？
Answers:
只需过滤目录中所需文件的事件即可：
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，我们检查更改后的文件是否为“ myFile.txt”，如果更改了，则执行任何操作。
OVERFLOW。您不需要注册。这里的例子。
不，无法注册文件，监视服务无法以这种方式工作。但是注册目录实际上会监视子目录（文件和子目录）上的更改，而不是目录本身上的更改。
如果要观看文件，请在观看服务中注册包含目录。Path.register（）文档说：
WatchKey java.nio.file.Path.register（WatchService watcher，Kind []事件，Modifier ...修饰符）引发IOException
用监视服务注册此路径下的文件。
在此版本中，此路径查找存在的目录。该目录已在监视服务中注册，以便可以监视目录中的条目
然后，您需要处理条目事件，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（实际上是条目的路径相对于其父路径的路径，这恰好是子名称）。你这里有一个例子。
其他答案是正确的，您必须监视目录并筛选特定文件。但是，您可能希望线程在后台运行。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
}
}
}
我尝试从公认的答案和本文中进行工作。您应该能够与此线程一起使用new FileWatcher(new File("/home/me/myfile")).start()并通过调用该线程来停止它stopThread()。
setDaemon(boolean)在调用之前run()根据您希望应用程序的行为进行。
Apache提供了带有方法的FileWatchDog类doOnChange。
private class SomeWatchFile extends FileWatchdog {
protected SomeWatchFile(String filename) {
super(filename);
}
@Override
protected void doOnChange() {
fileChanged= true;
}
}
在任何需要的地方都可以启动此线程：
SomeWatchFile someWatchFile = new SomeWatchFile (path);
someWatchFile.start();
FileWatchDog类轮询文件的lastModified()时间戳。Java NIO的本机WatchService效率更高，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课程实现：
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();
}
要使用此方法，您只需要扩展并实现如下onModified()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，开始查看文件：
String watchFile = System.getProperty("user.home") + File.separator + "Desktop" + File.separator + "Test.txt";
FileWatcher fileWatcher = new MyFileWatcher(watchFile);
fileWatcher.watchFile();
Not sure about others, but I groan at the amount of code needed to watch a single file for changes using the basic WatchService API. It has to be simpler!
Here are a couple of alternatives using third party libraries:
I have created a wrapper around Java 1.7's WatchService that allows registering a directory and any number of glob patterns. This class will take care of the filtering and only emit events you are interested in.
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);
}
Complete code is in this repo.