/src/mpv5/utils/files/FileMonitor.java

  1// Copyright (C) 2007 Google Inc.
  2//
  3// Licensed under the Apache License, Version 2.0 (the "License");
  4// you may not use this file except in compliance with the License.
  5// You may obtain a copy of the License at
  6//
  7// http://www.apache.org/licenses/LICENSE-2.0
  8//
  9// Unless required by applicable law or agreed to in writing, software
 10// distributed under the License is distributed on an "AS IS" BASIS,
 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 12// See the License for the specific language governing permissions and
 13// limitations under the License.
 14
 15package mpv5.utils.files;
 16
 17import java.io.File;
 18import java.util.HashMap;
 19import java.util.Timer;
 20import java.util.TimerTask;
 21
 22/**
 23 * Monitor files for changes. This singleton class maintains a map of files to
 24 * monitor and objects to notify when something they change.
 25 */
 26public class FileMonitor {
 27
 28  private static final FileMonitor SINGLETON = new FileMonitor();
 29
 30  private Timer timer;
 31  private HashMap<String, TimerTask> timerTasks;
 32
 33  private FileMonitor() {
 34    timer = new Timer(true);
 35    timerTasks = new HashMap<String, TimerTask>();
 36  }
 37
 38  /**
 39   * Returns the singleton instance of this class.
 40   * @return the singleton instance
 41   */
 42  public static FileMonitor getInstance() {
 43    return SINGLETON;
 44  }
 45
 46  /**
 47   * Start monitoring a file.
 48   * 
 49   * @param listener listener to notify when the file changed.
 50   * @param fileName name of the file to monitor.
 51   * @param period polling period in milliseconds.
 52   */
 53  public void addFileChangeListener(FileChangeListener listener,
 54      String fileName, long period) {
 55    removeFileChangeListener(listener, fileName);
 56    FileMonitorTask task = new FileMonitorTask(listener, fileName);
 57    timerTasks.put(fileName + listener.hashCode(), task);
 58    timer.schedule(task, period, period);
 59  }
 60
 61  /**
 62   * Remove the listener from the notification list.
 63   * 
 64   * @param listener the listener to be removed.
 65   */
 66  public void removeFileChangeListener(FileChangeListener listener,
 67      String fileName) {
 68    FileMonitorTask task = (FileMonitorTask) timerTasks.remove(fileName
 69        + listener.hashCode());
 70    if (task != null) {
 71      task.cancel();
 72    }
 73  }
 74
 75  protected void fireFileChangeEvent(FileChangeListener listener,
 76      String fileName) {
 77    listener.fileChanged(fileName);
 78  }
 79
 80  class FileMonitorTask extends TimerTask {
 81    FileChangeListener listener;
 82    String fileName;
 83    File monitoredFile;
 84    long lastModified;
 85
 86    public FileMonitorTask(FileChangeListener listener, String fileName) {
 87      this.listener = listener;
 88      this.fileName = fileName;
 89      this.lastModified = 0;
 90      monitoredFile = new File(fileName);
 91      this.lastModified = getLastModified();
 92    }
 93
 94    private long getLastModified() {
 95      if (monitoredFile.exists()) { 
 96        return monitoredFile.lastModified();
 97      } else {
 98        return -1;
 99      }
100    }
101
102    @Override
103    public void run() {
104      long lastModifiedInt = getLastModified();
105      if (lastModifiedInt != this.lastModified) {
106        this.lastModified = lastModifiedInt;
107        fireFileChangeEvent(this.listener, this.fileName);
108      }
109    }
110  }
111  
112  public interface FileChangeListener {
113    public void fileChanged(String fileName);
114  }
115}