我正在使用来自Oracle的WatchService示例：
import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.*;
import static java.nio.file.LinkOption.*;
import java.nio.file.attribute.*;
import java.io.*;
import java.util.*;
public class WatchDir {
private final WatchService watcher;
private final Map<WatchKey,Path> keys;
private final boolean recursive;
private boolean trace = false;
@SuppressWarnings("unchecked")
static <T> WatchEvent<T> cast(WatchEvent<?> event) {
return (WatchEvent<T>)event;
}
/**
* Register the given directory with the WatchService
*/
private void register(Path dir) throws IOException {
WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
if (trace) {
Path prev = keys.get(key);
if (prev == null) {
System.out.format("register: %s\n", dir);
} else {
if (!dir.equals(prev)) {
System.out.format("update: %s -> %s\n", prev, dir);
}
}
}
keys.put(key, dir);
}
/**
* Register the given directory, and all its sub-directories, with the
* WatchService.
*/
private void registerAll(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
@Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
throws IOException
{
register(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Creates a WatchService and registers the given directory
*/
WatchDir(Path dir, boolean recursive) throws IOException {
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey,Path>();
this.recursive = recursive;
if (recursive) {
System.out.format("Scanning %s ...\n", dir);
registerAll(dir);
System.out.println("Done.");
} else {
register(dir);
}
// enable trace after initial registration
this.trace = true;
}
/**
* Process all events for keys queued to the watcher
*/
void processEvents() {
for (;;) {
// wait for key to be signalled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
return;
}
Path dir = keys.get(key);
if (dir == null) {
System.err.println("WatchKey not recognized!!");
continue;
}
for (WatchEvent<?> event: key.pollEvents()) {
WatchEvent.Kind kind = event.kind();
// TBD - provide example of how OVERFLOW event is handled
if (kind == OVERFLOW) {
continue;
}
// Context for directory entry event is the file name of entry
WatchEvent<Path> ev = cast(event);
Path name = ev.context();
Path child = dir.resolve(name);
// print out event
System.out.format("%s: %s\n", event.kind().name(), child);
// if directory is created, and watching recursively, then
// register it and its sub-directories
if (recursive && (kind == ENTRY_CREATE)) {
try {
if (Files.isDirectory(child, NOFOLLOW_LINKS)) {
registerAll(child);
}
} catch (IOException x) {
// ignore to keep sample readbale
}
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
}
}
static void usage() {
System.err.println("usage: java WatchDir [-r] dir");
System.exit(-1);
}
public static void main(String[] args) throws IOException {
// parse arguments
if (args.length == 0 || args.length > 2)
usage();
boolean recursive = false;
int dirArg = 0;
if (args[0].equals("-r")) {
if (args.length < 2)
usage();
recursive = true;
dirArg++;
}
// register directory and process its events
Path dir = Paths.get(args[dirArg]);
new WatchDir(dir, recursive).processEvents();
}
}
我正在
Windows 7 中开发一个应用程序，部署环境是 rhel 7.2。在两个操作系统中，每当我复制一个文件时，它都会触发一个 ENTRY_CREATED 事件，然后触发两个 ENTRY_MODIFY 事件。第一个 ENTRY_MODIFY 出现在开始复制文件时，第二个 ENTRY_MODIFY 出现在复制结束时，因此我能够理解复制过程何时结束。但是，现在在 rhel 7.2 中只会触发一个 ENTRY_MODIFY 事件。但是在 Windows 7 中仍然会触发两个 ENTRY_MODIFY 事件。我在
stackoverflow 上找到了这个问题。该问题问为什么会出现两个 ENTRY_MODIFY 事件，虽然不完全是我的问题，但其中一些答案驳斥了我的问题。可惜，在那场争论中没有解决我的问题。由于在复制结束时没有触发
ENTRY_MODIFY 事件，我无法确定复制何时结束。你认为这可能是什么原因？这可以修复吗？我能如何确定复制已经结束？除了 rhel 7.2，我都可以接受任何其他解决方案。谢谢！
ENTRY_CREATED事件）后对其进行锁定。一旦该文件不再被复制进程锁定，锁定将被授予。此时，复制过程已完成。 - TT.