wamblee.org Git - utils/blob - support/general/src/main/java/org/wamblee/io/DirectoryMonitor.java

   1 /*
   2  * Copyright 2006 the original author or authors.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *      http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 package org.wamblee.io;
  18
  19 import java.io.File;
  20 import java.io.FileFilter;
  21 import java.util.Date;
  22 import java.util.HashMap;
  23 import java.util.HashSet;
  24 import java.util.Map;
  25 import java.util.Set;
  26
  27 import org.apache.commons.logging.Log;
  28 import org.apache.commons.logging.LogFactory;
  29
  30 /**
  31  * Monitors a directory for changes.
  32  *
  33  * @author Erik Brakkee
  34  */
  35 public class DirectoryMonitor {
  36
  37         private static final Log LOG = LogFactory.getLog(DirectoryMonitor.class);
  38
  39         public static interface Listener {
  40
  41                 void fileChanged(File aFile);
  42
  43                 void fileCreated(File aFile);
  44
  45                 void fileDeleted(File aFile);
  46         };
  47
  48         private File _directory;
  49         private FileFilter _filter;
  50         private Listener _listener;
  51         private Map<File, Date> _contents;
  52
  53         public DirectoryMonitor(File aDirectory, FileFilter aFilefilter,
  54                         Listener aListener) {
  55                 _directory = aDirectory;
  56                 if (!_directory.isDirectory()) {
  57                         throw new IllegalArgumentException("Directory '" + _directory
  58                                         + "' does not exist");
  59                 }
  60                 _filter = aFilefilter;
  61                 _listener = aListener;
  62                 _contents = new HashMap<File, Date>();
  63         }
  64
  65         /**
  66          * Polls the directory for changes and notifies the listener of any changes.
  67          * In case of any exceptions thrown by the listener while handling the changes,
  68          * the next call to this method will invoked the listeners again for the same changes.
  69          */
  70         public void poll() {
  71                 LOG.debug("Polling " + _directory);
  72                 Map<File, Date> newContents = new HashMap<File, Date>();
  73                 File[] files = _directory.listFiles(_filter);
  74
  75                 // Check deleted files.
  76                 Set<File> deletedFiles = new HashSet<File>(_contents.keySet());
  77                 for (File file : files) {
  78                         if (file.isFile()) {
  79                                 if (_contents.containsKey(file)) {
  80                                         deletedFiles.remove(file);
  81                                 }
  82                         }
  83                 }
  84                 for (File file : deletedFiles) {
  85                         _listener.fileDeleted(file);
  86                 }
  87
  88                 for (File file : files) {
  89                         if (file.isFile()) {
  90                                 if (_contents.containsKey(file)) {
  91                                         Date oldDate = _contents.get(file);
  92                                         if (file.lastModified() != oldDate.getTime()) {
  93                                                 _listener.fileChanged(file);
  94                                         } else {
  95                                                 // No change.
  96                                         }
  97                                         newContents.put(file, new Date(file.lastModified()));
  98                                 } else {
  99                                         _listener.fileCreated(file);
 100                                         newContents.put(file, new Date(file.lastModified()));
 101                                 }
 102                         }
 103                 }
 104
 105                 _contents = newContents;
 106         }
 107
 108 }