| package com.howtodoinjava.examples;
import static java.nio.file.StandardWatchEventKinds.*;
import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.HashMap;
import java.util.Map;
public class Java8WatchServiceExample {
private final WatchService watcher;
private final Map<WatchKey, Path> keys;
/**
* Creates a WatchService and registers the given directory
*/
Java8WatchServiceExample(Path dir) throws IOException {
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey, Path>();
walkAndRegisterDirectories(dir);
}
/**
* Register the given directory with the WatchService; This function will be called by FileVisitor
*/
private void registerDirectory(Path dir) throws IOException
{
WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
keys.put(key, dir);
}
/**
* Register the given directory, and all its sub-directories, with the WatchService.
*/
private void walkAndRegisterDirectories(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
@Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throwsIOException {
registerDirectory(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* 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()) {
@SuppressWarnings("rawtypes")
WatchEvent.Kind kind = event.kind();
// Context for directory entry event is the file name of entry
@SuppressWarnings("unchecked")
Path name = ((WatchEvent<Path>)event).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 (kind == ENTRY_CREATE) {
try {
if (Files.isDirectory(child)) {
walkAndRegisterDirectories(child);
}
} catch (IOException x) {
// do something useful
}
}
}
// 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;
}
}
}
}
public static void main(String[] args) throws IOException {
Path dir = Paths.get("c:/temp");
new Java8WatchServiceExample(dir).processEvents();
}
}
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