1 /* FileBasedPreferences.java -- File-based preference implementation
2    Copyright (C) 2006 Free Software Foundation, Inc.
3 
4 This file is part of GNU Classpath.
5 
6 GNU Classpath is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
9 any later version.
10 
11 GNU Classpath is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14 General Public License for more details.
15 
16 You should have received a copy of the GNU General Public License
17 along with GNU Classpath; see the file COPYING.  If not, write to the
18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
19 02110-1301 USA.
20 
21 Linking this library statically or dynamically with other modules is
22 making a combined work based on this library.  Thus, the terms and
23 conditions of the GNU General Public License cover the whole
24 combination.
25 
26 As a special exception, the copyright holders of this library give you
27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
29 modules, and to copy and distribute the resulting executable under
30 terms of your choice, provided that you also meet, for each linked
31 independent module, the terms and conditions of the license of that
32 module.  An independent module is a module which is not derived from
33 or based on this library.  If you modify this library, you may extend
34 this exception to your version of the library, but you are not
35 obligated to do so.  If you do not wish to do so, delete this
36 exception statement from your version. */
37 
38 
39 package gnu.java.util.prefs;
40 
41 import gnu.classpath.SystemProperties;
42 
43 import java.io.File;
44 import java.io.FileInputStream;
45 import java.io.FileOutputStream;
46 import java.io.FilenameFilter;
47 import java.io.IOException;
48 import java.nio.channels.FileChannel;
49 import java.nio.channels.FileLock;
50 import java.util.Properties;
51 import java.util.prefs.AbstractPreferences;
52 import java.util.prefs.BackingStoreException;
53 
54 /**
55  * This is a simple file-based preference implementation which writes
56  * the preferences as properties files.  A node is represented as a directory
57  * beneath the user's home directory.  The preferences for the node are
58  * stored in a single properties file in that directory.  Sub-nodes are
59  * stored in subdirectories.  This implementation uses file locking to
60  * mediate access to the properties files.
61  */
62 public class FileBasedPreferences
63     extends AbstractPreferences
64 {
65   /**
66    * Name of the property file storing the data in a given directory.
67    */
68   private static final String DATA_FILE = "data.properties";
69 
70   /**
71    * The directory corresponding to this preference node.
72    */
73   private File directory;
74 
75   /**
76    * The file holding the data for this node.
77    */
78   private File dataFile;
79 
80   /**
81    * The data in this node.
82    */
83   private Properties properties;
84 
85   /**
86    * Create the root node for the file-based preferences.
87    */
FileBasedPreferences()88   FileBasedPreferences()
89   {
90     super(null, "");
91     String home = SystemProperties.getProperty("user.home");
92     this.directory = new File(new File(home, ".classpath"), "userPrefs");
93     this.dataFile = new File(this.directory, DATA_FILE);
94     load();
95   }
96 
97   /**
98    * Create a new file-based preference object with the given parent
99    * and the given name.
100    * @param parent the parent
101    * @param name the name of this node
102    */
FileBasedPreferences(FileBasedPreferences parent, String name)103   FileBasedPreferences(FileBasedPreferences parent, String name)
104   {
105     super(parent, name);
106     this.directory = new File(parent.directory, name);
107     this.dataFile = new File(this.directory, DATA_FILE);
108     load();
109   }
110 
load()111   private void load()
112   {
113     this.properties = new Properties();
114     FileInputStream fis = null;
115     FileLock lock = null;
116     try
117       {
118         fis = new FileInputStream(this.dataFile);
119         FileChannel channel = fis.getChannel();
120         lock = channel.lock(0, Long.MAX_VALUE, true);
121         this.properties.load(fis);
122         // We release the lock and close the stream in the 'finally'
123         // clause.
124       }
125     catch (IOException _)
126       {
127         // We don't mind; this means we're making a new node.
128         newNode = true;
129       }
130     finally
131       {
132         try
133           {
134             // Release the lock and close the stream.
135             if (lock != null)
136               lock.release();
137           }
138         catch (IOException ignore)
139           {
140             // Ignore.
141           }
142         try
143           {
144             // Close the stream.
145             if (fis != null)
146               fis.close();
147           }
148         catch (IOException ignore)
149           {
150             // Ignore.
151           }
152       }
153   }
154 
isUserNode()155   public boolean isUserNode()
156   {
157     // For now file preferences are always user nodes.
158     return true;
159   }
160 
childrenNamesSpi()161   protected String[] childrenNamesSpi() throws BackingStoreException
162   {
163     // FIXME: security manager.
164     String[] result = directory.list(new FilenameFilter()
165                           {
166                             public boolean accept(File dir, String name)
167                             {
168                               return new File(dir, name).isDirectory();
169                             }
170                           });
171     if (result == null)
172       result = new String[0];
173     return result;
174   }
175 
childSpi(String name)176   protected AbstractPreferences childSpi(String name)
177   {
178     return new FileBasedPreferences(this, name);
179   }
180 
keysSpi()181   protected String[] keysSpi() throws BackingStoreException
182   {
183     return (String[]) properties.keySet().toArray(new String[0]);
184   }
185 
getSpi(String key)186   protected String getSpi(String key)
187   {
188     return properties.getProperty(key);
189   }
190 
putSpi(String key, String value)191   protected void putSpi(String key, String value)
192   {
193     properties.put(key, value);
194   }
195 
removeSpi(String key)196   protected void removeSpi(String key)
197   {
198     properties.remove(key);
199   }
200 
flushSpi()201   protected void flushSpi() throws BackingStoreException
202   {
203     // FIXME: security manager.
204     try
205       {
206         if (isRemoved())
207           {
208             // Delete the underlying file.
209             // FIXME: ideally we would also delete the directory
210             // if it had no subdirectories.  This doesn't matter
211             // much though.
212             // FIXME: there's a strange race here if a different VM is
213             // simultaneously updating this node.
214             dataFile.delete();
215           }
216         else
217           {
218             // Write the underlying file.
219             directory.mkdirs();
220 
221             FileOutputStream fos = null;
222             FileLock lock = null;
223             try
224               {
225                 // Note that we let IOExceptions from the try clause
226                 // propagate to the outer 'try'.
227                 fos = new FileOutputStream(dataFile);
228                 FileChannel channel = fos.getChannel();
229                 lock = channel.lock();
230                 properties.store(fos, "created by GNU Classpath FileBasedPreferences");
231                 // Lock is released and file closed in the finally clause.
232               }
233             finally
234               {
235                 try
236                   {
237                     if (lock != null)
238                       lock.release();
239                   }
240                 catch (IOException _)
241                   {
242                     // Ignore.
243                   }
244                 try
245                   {
246                     if (fos != null)
247                       fos.close();
248                   }
249                 catch (IOException _)
250                   {
251                     // Ignore.
252                   }
253               }
254           }
255       }
256     catch (IOException ioe)
257       {
258         throw new BackingStoreException(ioe);
259       }
260   }
261 
syncSpi()262   protected void syncSpi() throws BackingStoreException
263   {
264     // FIXME: we ought to synchronize but instead we merely flush.
265     flushSpi();
266   }
267 
removeNodeSpi()268   protected void removeNodeSpi() throws BackingStoreException
269   {
270     // We can simply delegate.
271     flushSpi();
272   }
273 }
274