KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > org > mule > util > monitor > FileMonitor


1 /*
2  * $Id: FileMonitor.java 3798 2006-11-04 04:07:14Z aperepel $
3  * --------------------------------------------------------------------------------------
4  * Copyright (c) MuleSource, Inc. All rights reserved. http://www.mulesource.com
5  *
6  * The software in this package is published under the terms of the MuleSource MPL
7  * license, a copy of which has been included with this distribution in the
8  * LICENSE.txt file.
9  */
10
11 package org.mule.util.monitor;
12
13 import java.beans.ExceptionListener JavaDoc;
14 import java.io.File JavaDoc;
15 import java.io.IOException JavaDoc;
16 import java.lang.ref.WeakReference JavaDoc;
17 import java.util.ArrayList JavaDoc;
18 import java.util.Collection JavaDoc;
19 import java.util.HashMap JavaDoc;
20 import java.util.Iterator JavaDoc;
21 import java.util.List JavaDoc;
22 import java.util.Map JavaDoc;
23 import java.util.Timer JavaDoc;
24 import java.util.TimerTask JavaDoc;
25
26 /**
27  * Class for monitoring changes in disk files. Usage: 1. Implement the FileListener
28  * interface. 2. Create a FileMonitor instance. 3. Add the file(s)/directory(ies) to
29  * listen for. fileChanged() will be called when a monitored file is created, deleted
30  * or its modified time changes.
31  *
32  * @author <a HREF="mailto:jacob.dreyer@geosoft.no">Jacob Dreyer</a>
33  */
34 public class FileMonitor
35 {
36     private Timer JavaDoc timer;
37     private Map JavaDoc files;
38     private List JavaDoc listeners;
39     private long pollingInterval;
40
41     /**
42      * Create a file monitor instance with specified polling interval.
43      *
44      * @param pollingInterval Polling interval in milli seconds.
45      */
46     public FileMonitor(long pollingInterval)
47     {
48         files = new HashMap JavaDoc();
49         listeners = new ArrayList JavaDoc();
50         timer = new Timer JavaDoc(true);
51         this.pollingInterval = pollingInterval;
52     }
53
54     /**
55      * Stop the file monitor polling.
56      */
57     public void stop()
58     {
59         timer.cancel();
60     }
61
62     public void start()
63     {
64         timer.schedule(new FileMonitorNotifier(), 0, pollingInterval);
65     }
66
67     /**
68      * Add file to listen for. File may be any java.io.File (including a directory)
69      * and may well be a non-existing file in the case where the creating of the file
70      * is to be trepped. <p/> More than one file can be listened for. When the
71      * specified file is created, modified or deleted, listeners are notified.
72      *
73      * @param file File to listen for.
74      */
75     public void addFile(File JavaDoc file)
76     {
77         if (!files.containsKey(file))
78         {
79             long modifiedTime = file.exists() ? file.lastModified() : -1;
80             files.put(file, new Long JavaDoc(modifiedTime));
81         }
82     }
83
84     /**
85      * Remove specified file for listening.
86      *
87      * @param file File to remove.
88      */
89     public void removeFile(File JavaDoc file)
90     {
91         files.remove(file);
92     }
93
94     /**
95      * Add listener to this file monitor.
96      *
97      * @param fileListener Listener to add.
98      */
99     public void addListener(FileListener fileListener)
100     {
101         // Don't add if its already there
102 for (Iterator JavaDoc i = listeners.iterator(); i.hasNext();)
103         {
104             WeakReference JavaDoc reference = (WeakReference JavaDoc)i.next();
105             FileListener listener = (FileListener)reference.get();
106             if (listener == fileListener)
107             {
108                 return;
109             }
110         }
111
112         // Use WeakReference to avoid memory leak if this becomes the
113 // sole reference to the object.
114 listeners.add(new WeakReference JavaDoc(fileListener));
115     }
116
117     /**
118      * Remove listener from this file monitor.
119      *
120      * @param fileListener Listener to remove.
121      */
122     public void removeListener(FileMonitor fileListener)
123     {
124         for (Iterator JavaDoc i = listeners.iterator(); i.hasNext();)
125         {
126             WeakReference JavaDoc reference = (WeakReference JavaDoc)i.next();
127             FileMonitor listener = (FileMonitor)reference.get();
128             if (listener == fileListener)
129             {
130                 i.remove();
131                 break;
132             }
133         }
134     }
135
136     /**
137      * This is the timer thread which is executed every n milliseconds according to
138      * the setting of the file monitor.
139      */
140     public class FileMonitorNotifier extends TimerTask JavaDoc
141     {
142         private ExceptionListener JavaDoc exceptionListener;
143
144         public FileMonitorNotifier()
145         {
146             super();
147         }
148
149         public FileMonitorNotifier(ExceptionListener JavaDoc exceptionListener)
150         {
151             this.exceptionListener = exceptionListener;
152         }
153
154         public void run()
155         {
156             // Loop over the registered files and see which have changed.
157 // Use a copy of the list in case listener wants to alter the
158 // list within its fileChanged method.
159 Collection JavaDoc fileKeys = new ArrayList JavaDoc(files.keySet());
160
161             for (Iterator JavaDoc i = fileKeys.iterator(); i.hasNext();)
162             {
163                 File JavaDoc file = (File JavaDoc)i.next();
164                 long lastModifiedTime = ((Long JavaDoc)files.get(file)).longValue();
165                 long newModifiedTime = file.exists() ? file.lastModified() : -1;
166
167                 // Chek if file has changed
168 if (newModifiedTime != lastModifiedTime)
169                 {
170                     // Register new modified time
171 files.put(file, new Long JavaDoc(newModifiedTime));
172
173                     // Notify listeners
174 for (Iterator JavaDoc j = listeners.iterator(); j.hasNext();)
175                     {
176                         WeakReference JavaDoc reference = (WeakReference JavaDoc)j.next();
177                         FileListener listener = (FileListener)reference.get();
178
179                         // Remove from list if the back-end object has been GC'd
180 if (listener == null)
181                         {
182                             j.remove();
183                         }
184                         else
185                         {
186                             try
187                             {
188                                 listener.fileChanged(file);
189                             }
190                             catch (IOException JavaDoc e)
191                             {
192                                 if (exceptionListener != null)
193                                 {
194                                     exceptionListener.exceptionThrown(e);
195                                 }
196                             }
197                         }
198                     }
199                 }
200             }
201         }
202     }
203 }
204
Popular Tags