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Jodd Core tools and utilities, including type converters, JDateTime, cache etc.
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// Copyright (c) 2003-2014, Jodd Team (jodd.org). All Rights Reserved.
package jodd.io;

import java.io.File;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.Timer;
import java.util.TimerTask;
import java.util.HashSet;

/**
 * Monitoring disk files changes. Change event is broadcasted to all registered listeners.
 *
 * @see jodd.io.FileChangeListener
 */
public class FileMonitor {

	protected final Map files;
	protected final Set listeners;
	protected final long pollingInterval;
	protected Timer timer;
	protected final Object lock = new Object();

	/**
	 * Creates a file monitor instance with specified polling interval in ms.
	 */
	public FileMonitor(long pollingInterval) {
		this.pollingInterval = pollingInterval;
		files = new HashMap();
		listeners = new HashSet();
		start();
	}

	/**
	 * Starts the file monitoring polling, after it was stopped.
	 */
	public void start() {
		if (timer == null) {
			timer = new Timer(true);
			timer.schedule(new FileMonitorNotifier(), 0, pollingInterval);
		}
	}

	/**
	 * Stops the file monitor polling.
	 */
	public void stop() {
		if (timer != null) {
			timer.cancel();
			timer = null;
		}
	}


	/**
	 * Adds file to listen for. File may be any file or folder,
	 * including a non-existing file in the case where the
	 * creating of the file is to be trapped.
	 */
	public void monitorFile(File file) {
		synchronized (lock) {
			if (files.containsKey(file) == false) {
				long modifiedTime = file.exists() ? file.lastModified() : -1;
				files.put(file, new Long(modifiedTime));
			}
		}
	}

	/**
	 * Removes specified file for listening.
	 */
	public void releaseFile(File file) {
		synchronized (lock) {
			files.remove(file);
		}
	}


	/**
	 * Adds listener to this file monitor.
	 */
	public void registerListener(FileChangeListener fileChangeListener) {
		synchronized (lock) {
			for (FileChangeListener listener : listeners) {
				if (listener == fileChangeListener) {
					return;
				}
			}
			listeners.add(fileChangeListener);
		}
	}


	/**
	 * Removes listener from this file monitor.
	 */
	public void removeListener(FileChangeListener fileChangeListener) {
		synchronized (lock) {
			Iterator i = listeners.iterator();
			while(i.hasNext()) {
				FileChangeListener listener = i.next();
				if (listener == fileChangeListener) {
					i.remove();
					break;
				}
			}
		}
	}

	/**
	 * Removes all file listeners/
	 */
	public void removeAllListeners() {
		synchronized (lock) {
			listeners.clear();
		}
	}


	/**
	 * Actual file monitor timer task.
	 */
	protected class FileMonitorNotifier extends TimerTask {

		@Override
		public void run() {
			synchronized (lock) {
				for (Map.Entry entry : files.entrySet()) {
					File file = entry.getKey();
					long lastModifiedTime = entry.getValue().longValue();
					long newModifiedTime = file.exists() ? file.lastModified() : -1;

					// check if file has been changed
					if (newModifiedTime != lastModifiedTime) {

						// store new modified time
						entry.setValue(new Long(newModifiedTime));

						// notify listeners
						for (FileChangeListener listener : listeners) {
							listener.onFileChange(file);
						}
					}
				}
			}
		}
	}

}