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| import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
import java.io.IOException;
import java.nio.file.ClosedWatchServiceException;
import java.nio.file.FileSystems;
import java.nio.file.FileVisitResult;
import java.nio.file.FileVisitor;
import java.nio.file.Files;
import java.nio.file.LinkOption;
import java.nio.file.Path;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* The recursive file watcher monitors a folder (and its sub-folders).
*
* <p>The class walks through the file tree and registers to a watch to every sub-folder.
* For new folders, a new watch is registered, and stale watches are removed.
*
* <p>When a file event occurs, a timer is started to wait for the file operations
* to settle. It is reset whenever a new event occurs. When the timer times out,
* an event is thrown through the {@link WatchListener}.
*
* @author Philipp C. Heckel <philipp.heckel@gmail.com>
*/
public class RecursiveWatcher {
private static final Logger logger = Logger.getLogger(RecursiveWatcher.class.getSimpleName());
private Path root;
private List<Path> ignorePaths;
private int settleDelay;
private WatchListener listener;
private AtomicBoolean running;
private WatchService watchService;
private Thread watchThread;
private Map<Path, WatchKey> watchPathKeyMap;
private Timer timer;
public RecursiveWatcher(Path root, List<Path> ignorePaths, int settleDelay, WatchListener listener) {
this.root = root;
this.ignorePaths = ignorePaths;
this.settleDelay = settleDelay;
this.listener = listener;
this.running = new AtomicBoolean(false);
this.watchService = null;
this.watchThread = null;
this.watchPathKeyMap = new HashMap<Path, WatchKey>();
this.timer = null;
}
/**
* Starts the watcher service and registers watches in all of the sub-folders of
* the given root folder.
*
* <p><b>Important:</b> This method returns immediately, even though the watches
* might not be in place yet. For large file trees, it might take several seconds
* until all directories are being monitored. For normal cases (1-100 folders), this
* should not take longer than a few milliseconds.
* @throws java.io.IOException
*/
public void start() throws IOException {
watchService = FileSystems.getDefault().newWatchService();
watchThread = new Thread(new Runnable() {
@Override
public void run() {
running.set(true);
walkTreeAndSetWatches();
while (running.get()) {
try {
WatchKey watchKey = watchService.take();
watchKey.pollEvents(); // Take events, but don't care what they are!
watchKey.reset();
resetWaitSettlementTimer();
}
catch (InterruptedException | ClosedWatchServiceException e) {
running.set(false);
}
}
}
}, "Watcher");
watchThread.start();
}
public synchronized void stop() {
if (watchThread != null) {
try {
watchService.close();
running.set(false);
watchThread.interrupt();
}
catch (IOException e) {
// Don't care
}
}
}
private synchronized void resetWaitSettlementTimer() {
logger.log(Level.FINE, "File system events registered. Waiting {0}ms for settlement ....", settleDelay);
if (timer != null) {
timer.cancel();
timer = null;
}
timer = new Timer("WatchTimer");
timer.schedule(new TimerTask() {
@Override
public void run() {
logger.log(Level.INFO, "File system actions (on watched folders) settled. Updating watches ...");
walkTreeAndSetWatches();
unregisterStaleWatches();
fireListenerEvents();
}
}, settleDelay);
}
private synchronized void walkTreeAndSetWatches() {
logger.log(Level.INFO, "Registering new folders at watch service ...");
try {
Files.walkFileTree(root, new FileVisitor<Path>() {
@Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
if (ignorePaths.contains(dir)) {
return FileVisitResult.SKIP_SUBTREE;
}
else {
registerWatch(dir);
return FileVisitResult.CONTINUE;
}
}
@Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
return FileVisitResult.CONTINUE;
}
@Override
public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
return FileVisitResult.CONTINUE;
}
});
}
catch (IOException e) {
// Don't care
}
}
private synchronized void unregisterStaleWatches() {
Set<Path> paths = new HashSet<Path>(watchPathKeyMap.keySet());
Set<Path> stalePaths = new HashSet<Path>();
for (Path path : paths) {
if (!Files.exists(path, LinkOption.NOFOLLOW_LINKS)) {
stalePaths.add(path);
}
}
if (stalePaths.size() > 0) {
logger.log(Level.INFO, "Cancelling stale path watches ...");
for (Path stalePath : stalePaths) {
unregisterWatch(stalePath);
}
}
}
private synchronized void fireListenerEvents() {
if (listener != null) {
logger.log(Level.INFO, "- Firing watch event (watchEventsOccurred) ...");
listener.watchEventsOccurred();
}
}
private synchronized void registerWatch(Path dir) {
if (!watchPathKeyMap.containsKey(dir)) {
logger.log(Level.INFO, "- Registering " + dir);
try {
WatchKey watchKey = dir.register(watchService, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY, OVERFLOW);
watchPathKeyMap.put(dir, watchKey);
}
catch (IOException e) {
// Don't care!
}
}
}
private synchronized void unregisterWatch(Path dir) {
WatchKey watchKey = watchPathKeyMap.get(dir);
if (watchKey != null) {
logger.log(Level.INFO, "- Cancelling " + dir);
watchKey.cancel();
watchPathKeyMap.remove(dir);
}
}
public interface WatchListener {
public void watchEventsOccurred();
}
} |
