Mega Code Archive
Monitoring a File for changes
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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);
}
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