jforum example source code file (FileMonitor.java)

This example jforum source code file (FileMonitor.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - jforum tags/keywords

file, file, filechangelistener, filemonitor, filemonitor, filemonitortask, filemonitortask, io, logger, map, string, string, timer, timertask, util, watching

The jforum FileMonitor.java source code

/*
 * Copyright (c) 2003, 2004 Rafael Steil
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, 
 * with or without modification, are permitted provided 
 * that the following conditions are met:
 * 
 * 1) Redistributions of source code must retain the above 
 * copyright notice, this list of conditions and the 
 * following  disclaimer.
 * 2)  Redistributions in binary form must reproduce the 
 * above copyright notice, this list of conditions and 
 * the following disclaimer in the documentation and/or 
 * other materials provided with the distribution.
 * 3) Neither the name of "Rafael Steil" nor 
 * the names of its contributors may be used to endorse 
 * or promote products derived from this software without 
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT 
 * HOLDERS AND CONTRIBUTORS "AS IS" AND ANY 
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, 
 * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR 
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL 
 * THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE 
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES 
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, 
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER 
 * IN CONTRACT, STRICT LIABILITY, OR TORT 
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE
 * 
 * Created on 02/06/2004 23:29:51
 * The JForum Project
 * http://www.jforum.net
 */
package net.jforum.util;

import java.io.File;
import java.util.HashMap;
import java.util.Map;
import java.util.Timer;
import java.util.TimerTask;

import org.apache.log4j.Logger;

/**
 * Monitor class for file changes.
 * 
 * @author Rafael Steil
 * @version $Id: FileMonitor.java,v 1.9 2007/04/12 02:11:53 rafaelsteil Exp $
 */
public class FileMonitor
{
	private static Logger logger = Logger.getLogger(FileMonitor.class);
	private static final FileMonitor instance = new FileMonitor();
	private Timer timer;
	private Map timerEntries;
	
	private FileMonitor() {
		this.timerEntries = new HashMap();
		this.timer = new Timer(true);
	}
	
	public static FileMonitor getInstance() {
		return instance;
	}
	
	/**
	 * Add a file to the monitor
	 * 
	 * @param listener The file listener
	 * @param filename The filename to watch
	 * @param period The watch interval.
	 */
	public void addFileChangeListener(FileChangeListener listener, 
		String filename, long period) {
		this.removeFileChangeListener(filename);
		
		logger.info("Watching " + filename);
		
		FileMonitorTask task = new FileMonitorTask(listener, filename);
		
		this.timerEntries.put(filename, task);
		this.timer.schedule(task, period, period);
	}
	
	/**
	 * Stop watching a file
	 * 
	 * @param listener The file listener
	 * @param filename The filename to keep watch
	 */
	public void removeFileChangeListener(String filename) {
		FileMonitorTask task = (FileMonitorTask)this.timerEntries.remove(filename);
		
		if (task != null) {
			task.cancel();
		}
	}
	
	private static class FileMonitorTask extends TimerTask {
		private FileChangeListener listener;
		private String filename;
		private File monitoredFile;
		private long lastModified;
		
		public FileMonitorTask(FileChangeListener listener, String filename) {
			this.listener = listener;
			this.filename = filename;
			
			this.monitoredFile = new File(filename);
			if (!this.monitoredFile.exists()) {
				return;
			}
			
			this.lastModified = this.monitoredFile.lastModified();
		}
		
		public void run() {
			long latestChange = this.monitoredFile.lastModified();
			if (this.lastModified != latestChange) {
				this.lastModified = latestChange;
				
				this.listener.fileChanged(this.filename);
			}
		}
	}
}