libjava/gnu/java/nio/charset/Provider.java

   1 /* Provider.java --
   2    Copyright (C) 2002, 2005 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., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 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 package gnu.java.nio.charset;
  39
  40 import java.nio.charset.Charset;
  41 import java.nio.charset.spi.CharsetProvider;
  42 import java.util.Collections;
  43 import java.util.HashMap;
  44 import java.util.Iterator;
  45
  46 /**
  47  * Charset provider for the required charsets.  Used by
  48  * {@link Charset#charsetForName} and * {@link Charset#availableCharsets}.
  49  *
  50  * @author Jesse Rosenstock
  51  * @author Robert Schuster (thebohemian@gmx.net)
  52  * @see Charset
  53  */
  54 public final class Provider extends CharsetProvider
  55 {
  56   private static Provider singleton;
  57
  58   static
  59   {
  60     synchronized (Provider.class)
  61       {
  62         singleton = null;
  63       }
  64   }
  65
  66   /**
  67    * Map from charset name to charset canonical name. The strings
  68    * are all lower-case to allow case-insensitive retrieval of
  69    * Charset instances.
  70    */
  71   private final HashMap canonicalNames;
  72
  73   /**
  74    * Map from lower-case canonical name to Charset.
  75    * TODO: We may want to use soft references.  We would then need to keep
  76    * track of the class name to regenerate the object.
  77    */
  78   private final HashMap charsets;
  79
  80   private Provider ()
  81   {
  82     canonicalNames = new HashMap ();
  83     charsets = new HashMap ();
  84
  85     // US-ASCII aka ISO646-US
  86     addCharset (new US_ASCII ());
  87
  88     // ISO-8859-1 aka ISO-LATIN-1
  89     addCharset (new ISO_8859_1 ());
  90
  91     // UTF-8
  92     addCharset (new UTF_8 ());
  93
  94     // UTF-16BE
  95     addCharset (new UTF_16BE ());
  96
  97     // UTF-16LE
  98     addCharset (new UTF_16LE ());
  99
 100     // UTF-16
 101     addCharset (new UTF_16 ());
 102   }
 103
 104   public Iterator charsets ()
 105   {
 106     return Collections.unmodifiableCollection (charsets.values ())
 107                       .iterator ();
 108   }
 109
 110   /**
 111    * Returns a Charset instance by converting the given
 112    * name to lower-case, looking up the canonical charset
 113    * name and finally looking up the Charset with that name.
 114    *
 115    * <p>The lookup is therefore case-insensitive.</p>
 116    *
 117    *  @returns The Charset having <code>charsetName</code>
 118    *  as its alias or null if no such Charset exist.
 119    */
 120   public Charset charsetForName (String charsetName)
 121   {
 122     return (Charset) charsets.get(canonicalNames.get(charsetName.toLowerCase()));
 123   }
 124
 125   /**
 126    * Puts a Charset under its canonical name into the 'charsets' map.
 127    * Then puts a mapping from all its alias names to the canonical name.
 128    *
 129    * <p>All names are converted to lower-case</p>.
 130    *
 131    * @param cs
 132    */
 133   private void addCharset (Charset cs)
 134   {
 135     String canonicalName = cs.name().toLowerCase();
 136     charsets.put (canonicalName, cs);
 137
 138     /* Adds a mapping between the canonical name
 139      * itself making a lookup using that name
 140      * no special case.
 141      */
 142     canonicalNames.put(canonicalName, canonicalName);
 143
 144     for (Iterator i = cs.aliases ().iterator (); i.hasNext (); )
 145       canonicalNames.put (((String) i.next()).toLowerCase(), canonicalName);
 146   }
 147
 148   public static synchronized Provider provider ()
 149   {
 150     if (singleton == null)
 151       singleton = new Provider ();
 152     return singleton;
 153   }
 154 }