FileWatcher.java

/**
 *  Copyright 2011 Oliver Buchtala
 *
 *	This file is part of ndogen.
 *
 *  ndogen is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  ndogen is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with ndogen.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.ndogen.watch;

import java.io.File;
import java.io.IOException;

public class FileWatcher implements Runnable {
	
	long lastModified;
	
	String lastHash;
	
	final static long refreshInterval = 1000;

	private File file;
	
	private final Runnable runner;
	
	boolean running;
	
	public FileWatcher(String filePath, Runnable runner) {
		this.runner = runner;
		file = new File(filePath);
	}

	@Override
	public void run() {
		
		this.running = true;
		
		while(running) {
			if(file.lastModified() != lastModified) {
				
				String fileHash = "";
				try {
					fileHash = FileUtils.getFileHash(file);
				
					if(!fileHash.equals(lastHash)) {
						// Note: these three actions are not atomar
						// 	so it may happen that the file changes while we
						//  process it
						// to take the modification info before processing
						// is the conservative strategy
						lastModified = file.lastModified();
						lastHash = fileHash;
						this.runner.run();
					}

				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			
			try {
				Thread.sleep(refreshInterval);
			} catch (InterruptedException e) {
			}
		}
	}
	
}