FileMonitor.java Source code

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Here is the source code for FileMonitor.java

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/*******************************************************************************
 * Copyright (c) 2007 Pascal Essiembre.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Pascal Essiembre - initial API and implementation
 ******************************************************************************/

import java.io.File;
import java.io.FileNotFoundException;
import java.net.URL;
import java.util.Hashtable;
import java.util.Timer;
import java.util.TimerTask;

/**
 * Class monitoring a {@link File} for changes.
 * 
 * @author Pascal Essiembre
 */
public class FileMonitor {

    private static final FileMonitor instance = new FileMonitor();

    private Timer timer;

    private Hashtable<String, FileMonitorTask> timerEntries;

    /**
     * Gets the file monitor instance.
     * 
     * @return file monitor instance
     */
    public static FileMonitor getInstance() {
        return instance;
    }

    /**
     * Constructor.
     */
    private FileMonitor() {
        // Create timer, run timer thread as daemon.
        timer = new Timer(true);
        timerEntries = new Hashtable<String, FileMonitorTask>();
    }

    /**
     * Adds a monitored file with a {@link FileChangeListener}.
     * 
     * @param listener
     *          listener to notify when the file changed.
     * @param fileName
     *          name of the file to monitor.
     * @param period
     *          polling period in milliseconds.
     */
    public void addFileChangeListener(FileChangeListener listener, String fileName, long period)
            throws FileNotFoundException {
        addFileChangeListener(listener, new File(fileName), period);
    }

    /**
     * Adds a monitored file with a FileChangeListener.
     * 
     * @param listener
     *          listener to notify when the file changed.
     * @param fileName
     *          name of the file to monitor.
     * @param period
     *          polling period in milliseconds.
     */
    public void addFileChangeListener(FileChangeListener listener, File file, long period)
            throws FileNotFoundException {
        removeFileChangeListener(listener, file);
        FileMonitorTask task = new FileMonitorTask(listener, file);
        timerEntries.put(file.toString() + listener.hashCode(), task);
        timer.schedule(task, period, period);
    }

    /**
     * Remove the listener from the notification list.
     * 
     * @param listener
     *          the listener to be removed.
     */
    public void removeFileChangeListener(FileChangeListener listener, String fileName) {
        removeFileChangeListener(listener, new File(fileName));
    }

    /**
     * Remove the listener from the notification list.
     * 
     * @param listener
     *          the listener to be removed.
     */
    public void removeFileChangeListener(FileChangeListener listener, File file) {
        FileMonitorTask task = timerEntries.remove(file.toString() + listener.hashCode());
        if (task != null) {
            task.cancel();
        }
    }

    /**
     * Fires notification that a file changed.
     * 
     * @param listener
     *          file change listener
     * @param file
     *          the file that changed
     */
    protected void fireFileChangeEvent(FileChangeListener listener, File file) {
        listener.fileChanged(file);
    }

    /**
     * File monitoring task.
     */
    class FileMonitorTask extends TimerTask {
        FileChangeListener listener;

        File monitoredFile;

        long lastModified;

        public FileMonitorTask(FileChangeListener listener, File file) throws FileNotFoundException {
            this.listener = listener;
            this.lastModified = 0;
            monitoredFile = file;
            if (!monitoredFile.exists()) { // but is it on CLASSPATH?
                URL fileURL = listener.getClass().getClassLoader().getResource(file.toString());
                if (fileURL != null) {
                    monitoredFile = new File(fileURL.getFile());
                } else {
                    throw new FileNotFoundException("File Not Found: " + file);
                }
            }
            this.lastModified = monitoredFile.lastModified();
        }

        public void run() {
            long lastModified = monitoredFile.lastModified();
            if (lastModified != this.lastModified) {
                this.lastModified = lastModified;
                fireFileChangeEvent(this.listener, monitoredFile);
            }
        }
    }
}

/*******************************************************************************
 * Copyright (c) 2007 Pascal Essiembre. All rights reserved. This program and
 * the accompanying materials are made available under the terms of the Eclipse
 * Public License v1.0 which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors: Pascal Essiembre - initial API and implementation
 ******************************************************************************/

/**
 * Listener interested in {@link File} changes.
 * 
 * @author Pascal Essiembre
 */
interface FileChangeListener {
    /**
     * Invoked when a file changes.
     * 
     * @param fileName
     *          name of changed file.
     */
    public void fileChanged(File file);
}