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1   package org.apache.turbine.services.localization;
2   
3   /*
4    * Copyright 2001-2005 The Apache Software Foundation.
5    *
6    * Licensed under the Apache License, Version 2.0 (the "License")
7    * you may not use this file except in compliance with the License.
8    * You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  import java.util.ArrayList;
20  import java.util.Collections;
21  import java.util.Iterator;
22  import java.util.Locale;
23  import java.util.NoSuchElementException;
24  import java.util.StringTokenizer;
25  
26  /***
27   * Parses the HTTP <code>Accept-Language</code> header as per section
28   * 14.4 of RFC 2068 (HTTP 1.1 header field definitions).
29   *
30   * @author <a href="mailto:dlr@collab.net">Daniel Rall</a>
31   * @version $Id: LocaleTokenizer.java 264148 2005-08-29 14:21:04Z henning $
32   */
33  public class LocaleTokenizer
34          implements Iterator
35  {
36      /***
37       * Separates elements of the <code>Accept-Language</code> HTTP
38       * header.
39       */
40      private static final String LOCALE_SEPARATOR = ",";
41  
42      /***
43       * Separates locale from quality within elements.
44       */
45      private static final char QUALITY_SEPARATOR = ';';
46  
47      /***
48       * The default quality value for an <code>AcceptLanguage</code>
49       * object.
50       */
51      private static final Float DEFAULT_QUALITY = new Float(1.0f);
52  
53      /***
54       * The parsed locales.
55       */
56      private ArrayList locales = new ArrayList(3);
57  
58      /***
59       * Parses the <code>Accept-Language</code> header.
60       *
61       * @param header The <code>Accept-Language</code> header
62       * (i.e. <code>en, es;q=0.8, zh-TW;q=0.1</code>).
63       */
64      public LocaleTokenizer(String header)
65      {
66          StringTokenizer tok = new StringTokenizer(header, LOCALE_SEPARATOR);
67          while (tok.hasMoreTokens())
68          {
69              AcceptLanguage acceptLang = new AcceptLanguage();
70              String element = tok.nextToken().trim();
71              int index;
72  
73              // Record and cut off any quality value that comes after a
74              // semi-colon.
75              if ((index = element.indexOf(QUALITY_SEPARATOR)) != -1)
76              {
77                  String q = element.substring(index);
78                  element = element.substring(0, index);
79                  if ((index = q.indexOf('=')) != -1)
80                  {
81                      try
82                      {
83                          acceptLang.quality =
84                                  Float.valueOf(q.substring(index + 1));
85                      }
86                      catch (NumberFormatException useDefault)
87                      {
88                      }
89                  }
90              }
91  
92              element = element.trim();
93  
94              // Create a Locale from the language.  A dash may separate the
95              // language from the country.
96              if ((index = element.indexOf('-')) == -1)
97              {
98                  // No dash means no country.
99                  acceptLang.locale = new Locale(element, "");
100             }
101             else
102             {
103                 acceptLang.locale = new Locale(element.substring(0, index),
104                         element.substring(index + 1));
105             }
106 
107             locales.add(acceptLang);
108         }
109 
110         // Sort by quality in descending order.
111         Collections.sort(locales, Collections.reverseOrder());
112     }
113 
114     /***
115      * @return Whether there are more locales.
116      */
117     public boolean hasNext()
118     {
119         return !locales.isEmpty();
120     }
121 
122     /***
123      * Creates a <code>Locale</code> from the next element of the
124      * <code>Accept-Language</code> header.
125      *
126      * @return The next highest-rated <code>Locale</code>.
127      * @throws NoSuchElementException No more locales.
128      */
129     public Object next()
130     {
131         if (locales.isEmpty())
132         {
133             throw new NoSuchElementException();
134         }
135         return ((AcceptLanguage) locales.remove(0)).locale;
136     }
137 
138     /***
139      * Not implemented.
140      */
141     public final void remove()
142     {
143         throw new UnsupportedOperationException(getClass().getName() +
144                 " does not support remove()");
145     }
146 
147     /***
148      * Struct representing an element of the HTTP
149      * <code>Accept-Language</code> header.
150      */
151     private class AcceptLanguage implements Comparable
152     {
153         /***
154          * The language and country.
155          */
156         Locale locale;
157 
158         /***
159          * The quality of our locale (as values approach
160          * <code>1.0</code>, they indicate increased user preference).
161          */
162         Float quality = DEFAULT_QUALITY;
163 
164         public final int compareTo(Object acceptLang)
165         {
166             return quality.compareTo(((AcceptLanguage) acceptLang).quality);
167         }
168     }
169 }