File Listener or Folder LIstener

Find out any file Created to  specific folder then go to the FileListener
interface:
----------

import java.io.File;



public interface FileListener

{

void fileChanged (File file);

}





class:

-----









import java.util.*;

import java.io.File;

import java.lang.ref.WeakReference;









/**

 * Class for monitoring changes in disk files.

 * Usage:

 *

 *    1. Implement the FileListener interface.

 *    2. Create a FileMonitor instance.

 *    3. Add the file(s)/directory(ies) to listen for.

 *

 * fileChanged() will be called when a monitored file is created,

 * deleted or its modified time changes.

 *

 * @author <a href="mailto:info@geosoft.no">GeoSoft</a>

 */

public class FileMonitor

{

  private Timer       timer_;

  private HashMap     files_;       // File -> Long

  private Collection  listeners_;   // of WeakReference(FileListener)






  /**

   * Create a file monitor instance with specified polling interval.

   *

   * @param pollingInterval  Polling interval in milli seconds.

   */

  public FileMonitor (long pollingInterval)

  {

    files_     = new HashMap();

    listeners_ = new ArrayList();



    timer_ = new Timer (true);

    timer_.schedule (new FileMonitorNotifier(), 0, pollingInterval);

  }







  /**

   * Stop the file monitor polling.

   */

  public void stop()

  {

    timer_.cancel();

  }





  /**

   * Add file to listen for. File may be any java.io.File (including a

   * directory) and may well be a non-existing file in the case where the

   * creating of the file is to be trepped.

   * <p>

   * More than one file can be listened for. When the specified file is

   * created, modified or deleted, listeners are notified.

   *

   * @param file  File to listen for.

   */

  public void addFile (File file)

  {

    if (!files_.containsKey (file)) {

      long modifiedTime = file.exists() ? file.lastModified() : -1;

      files_.put (file, new Long (modifiedTime));

    }

  }







  /**

   * Remove specified file for listening.

   *

   * @param file  File to remove.

   */

  public void removeFile (File file)

  {

    files_.remove (file);

  }







  /**

   * Add listener to this file monitor.

   *

   * @param fileListener  Listener to add.

   */

  public void addListener (FileListener fileListener)

  {

    // Don't add if its already there

    for (Iterator i = listeners_.iterator(); i.hasNext(); ) {

      WeakReference reference = (WeakReference) i.next();

      FileListener listener = (FileListener) reference.get();

      if (listener == fileListener)

        return;

    }



    // Use WeakReference to avoid memory leak if this becomes the

    // sole reference to the object.

    listeners_.add (new WeakReference (fileListener));

  }







  /**

   * Remove listener from this file monitor.

   *

   * @param fileListener  Listener to remove.

   */

  public void removeListener (FileListener fileListener)

  {

    for (Iterator i = listeners_.iterator(); i.hasNext(); ) {

      WeakReference reference = (WeakReference) i.next();

      FileListener listener = (FileListener) reference.get();

      if (listener == fileListener) {

        i.remove();

        break;

      }

    }

  }







  /**

   * This is the timer thread which is executed every n milliseconds

   * according to the setting of the file monitor. It investigates the

   * file in question and notify listeners if changed.

   */

  private class FileMonitorNotifier extends TimerTask

  {

    public void run()

    {

      // Loop over the registered files and see which have changed.

      // Use a copy of the list in case listener wants to alter the

      // list within its fileChanged method.

      Collection files = new ArrayList (files_.keySet());

   

      for (Iterator i = files.iterator(); i.hasNext(); ) {

        File file = (File) i.next();

        long lastModifiedTime = ((Long) files_.get (file)).longValue();

        long newModifiedTime  = file.exists() ? file.lastModified() : -1;



        // Chek if file has changed

        if (newModifiedTime != lastModifiedTime) {



          // Register new modified time

          files_.put (file, new Long (newModifiedTime));



          // Notify listeners

          for (Iterator j = listeners_.iterator(); j.hasNext(); ) {

            WeakReference reference = (WeakReference) j.next();

            FileListener listener = (FileListener) reference.get();



            // Remove from list if the back-end object has been GC'd

            if (listener == null)

              j.remove();

            else

              listener.fileChanged (file);

          }

        }

      }

    }

  }





  /**

   * Test this class.

   *

   * @param args  Not used.

   */

  public static void main (String args[])

  {

    // Create the monitor

    FileMonitor monitor = new FileMonitor (1000);



    // Add some files to listen for




    monitor.addFile (new File ("C:/Users/Home/Desktop/listerners/"));  



    // Add a dummy listener

    monitor.addListener (monitor.new TestListener());



    // Avoid program exit

    while (!false) ;

  }





  private class TestListener

    implements FileListener

  {

    public void fileChanged (File file)

    {

      System.out.println ("File changed: " + file);

    }

  }

}