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.ArrayList;
  22 import java.util.Date;
  23 import java.util.HashMap;
  24 import java.util.HashSet;
  25 import java.util.List;
  26 import java.util.Map;
  27 import java.util.Set;
  28
  29 import org.apache.commons.logging.Log;
  30 import org.apache.commons.logging.LogFactory;
  31
  32 /**
  33  * Monitors a directory for changes.
  34  *
  35  * @author Erik Brakkee
  36  */
  37 public class DirectoryMonitor {
  38
  39         private static final Log LOG = LogFactory.getLog(DirectoryMonitor.class);
  40
  41         public static interface Listener {
  42
  43                 void fileChanged(File aFile);
  44
  45                 void fileCreated(File aFile);
  46
  47                 void fileDeleted(File aFile);
  48         };
  49
  50         private File _directory;
  51         private FileFilter _filter;
  52         private Listener _listener;
  53         private Map<File, Date> _contents;
  54
  55         public DirectoryMonitor(File aDirectory, FileFilter aFilefilter,
  56                         Listener aListener) {
  57                 _directory = aDirectory;
  58                 if (!_directory.isDirectory()) {
  59                         throw new IllegalArgumentException("Directory '" + _directory
  60                                         + "' does not exist");
  61                 }
  62                 _filter = aFilefilter;
  63                 _listener = aListener;
  64                 _contents = new HashMap<File, Date>();
  65         }
  66
  67         /**
  68          * Polls the directory for changes and notifies the listener of any changes.
  69          * In case of any exceptions thrown by the listener while handling the changes,
  70          * the next call to this method will invoked the listeners again for the same changes.
  71          */
  72         public void poll() {
  73                 LOG.debug("Polling " + _directory);
  74                 Map<File, Date> newContents = new HashMap<File, Date>();
  75                 File[] files = _directory.listFiles(_filter);
  76
  77                 // Check deleted files.
  78                 Set<File> deletedFiles = new HashSet<File>(_contents.keySet());
  79                 for (File file : files) {
  80                         if (file.isFile()) {
  81                                 if (_contents.containsKey(file)) {
  82                                         deletedFiles.remove(file);
  83                                 }
  84                         }
  85                 }
  86                 for (File file : deletedFiles) {
  87                         _listener.fileDeleted(file);
  88                 }
  89
  90                 for (File file : files) {
  91                         if (file.isFile()) {
  92                                 if (_contents.containsKey(file)) {
  93                                         Date oldDate = _contents.get(file);
  94                                         if (file.lastModified() != oldDate.getTime()) {
  95                                                 _listener.fileChanged(file);
  96                                         } else {
  97                                                 // No change.
  98                                         }
  99                                         newContents.put(file, new Date(file.lastModified()));
 100                                 } else {
 101                                         _listener.fileCreated(file);
 102                                         newContents.put(file, new Date(file.lastModified()));
 103                                 }
 104                         }
 105                 }
 106
 107                 _contents = newContents;
 108         }
 109
 110 }