001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 * 
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 * 
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.io;
018
019import java.nio.charset.Charset;
020import java.nio.charset.UnsupportedCharsetException;
021import java.util.Collections;
022import java.util.SortedMap;
023import java.util.TreeMap;
024
025/**
026 * Charsets required of every implementation of the Java platform.
027 * 
028 * From the Java documentation <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">
029 * Standard charsets</a>:
030 * <p>
031 * <cite>Every implementation of the Java platform is required to support the following character encodings. Consult
032 * the release documentation for your implementation to see if any other encodings are supported. Consult the release
033 * documentation for your implementation to see if any other encodings are supported. </cite>
034 * </p>
035 * 
036 * <ul>
037 * <li><code>US-ASCII</code><br>
038 * Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the Unicode character set.</li>
039 * <li><code>ISO-8859-1</code><br>
040 * ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.</li>
041 * <li><code>UTF-8</code><br>
042 * Eight-bit Unicode Transformation Format.</li>
043 * <li><code>UTF-16BE</code><br>
044 * Sixteen-bit Unicode Transformation Format, big-endian byte order.</li>
045 * <li><code>UTF-16LE</code><br>
046 * Sixteen-bit Unicode Transformation Format, little-endian byte order.</li>
047 * <li><code>UTF-16</code><br>
048 * Sixteen-bit Unicode Transformation Format, byte order specified by a mandatory initial byte-order mark (either order
049 * accepted on input, big-endian used on output.)</li>
050 * </ul>
051 * 
052 * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
053 * @since 2.3
054 * @version $Id: Charsets.java 1563227 2014-01-31 19:45:30Z ggregory $
055 */
056public class Charsets {
057    //
058    // This class should only contain Charset instances for required encodings. This guarantees that it will load
059    // correctly and without delay on all Java platforms.
060    //
061
062    /**
063     * Constructs a sorted map from canonical charset names to charset objects required of every implementation of the
064     * Java platform.
065     * <p>
066     * From the Java documentation <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">
067     * Standard charsets</a>:
068     * </p>
069     * 
070     * @return An immutable, case-insensitive map from canonical charset names to charset objects.
071     * @see Charset#availableCharsets()
072     * @since 2.5
073     */
074    public static SortedMap<String, Charset> requiredCharsets() {
075        // maybe cache?
076        // TODO Re-implement on Java 7 to use java.nio.charset.StandardCharsets
077        final TreeMap<String, Charset> m = new TreeMap<String, Charset>(String.CASE_INSENSITIVE_ORDER);
078        m.put(ISO_8859_1.name(), ISO_8859_1);
079        m.put(US_ASCII.name(), US_ASCII);
080        m.put(UTF_16.name(), UTF_16);
081        m.put(UTF_16BE.name(), UTF_16BE);
082        m.put(UTF_16LE.name(), UTF_16LE);
083        m.put(UTF_8.name(), UTF_8);
084        return Collections.unmodifiableSortedMap(m);
085    }
086
087    /**
088     * Returns the given Charset or the default Charset if the given Charset is null.
089     * 
090     * @param charset
091     *            A charset or null.
092     * @return the given Charset or the default Charset if the given Charset is null
093     */
094    public static Charset toCharset(final Charset charset) {
095        return charset == null ? Charset.defaultCharset() : charset;
096    }
097
098    /**
099     * Returns a Charset for the named charset. If the name is null, return the default Charset.
100     * 
101     * @param charset
102     *            The name of the requested charset, may be null.
103     * @return a Charset for the named charset
104     * @throws UnsupportedCharsetException
105     *             If the named charset is unavailable
106     */
107    public static Charset toCharset(final String charset) {
108        return charset == null ? Charset.defaultCharset() : Charset.forName(charset);
109    }
110
111    /**
112     * CharEncodingISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.
113     * <p>
114     * Every implementation of the Java platform is required to support this character encoding.
115     * </p>
116     * 
117     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
118     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
119     */
120    @Deprecated
121    public static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");
122
123    /**
124     * <p>
125     * Seven-bit ASCII, also known as ISO646-US, also known as the Basic Latin block of the Unicode character set.
126     * </p>
127     * <p>
128     * Every implementation of the Java platform is required to support this character encoding.
129     * </p>
130     * 
131     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
132     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
133     */
134    @Deprecated
135    public static final Charset US_ASCII = Charset.forName("US-ASCII");
136
137    /**
138     * <p>
139     * Sixteen-bit Unicode Transformation Format, The byte order specified by a mandatory initial byte-order mark
140     * (either order accepted on input, big-endian used on output)
141     * </p>
142     * <p>
143     * Every implementation of the Java platform is required to support this character encoding.
144     * </p>
145     * 
146     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
147     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
148     */
149    @Deprecated
150    public static final Charset UTF_16 = Charset.forName("UTF-16");
151
152    /**
153     * <p>
154     * Sixteen-bit Unicode Transformation Format, big-endian byte order.
155     * </p>
156     * <p>
157     * Every implementation of the Java platform is required to support this character encoding.
158     * </p>
159     * 
160     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
161     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
162     */
163    @Deprecated
164    public static final Charset UTF_16BE = Charset.forName("UTF-16BE");
165
166    /**
167     * <p>
168     * Sixteen-bit Unicode Transformation Format, little-endian byte order.
169     * </p>
170     * <p>
171     * Every implementation of the Java platform is required to support this character encoding.
172     * </p>
173     * 
174     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
175     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
176     */
177    @Deprecated
178    public static final Charset UTF_16LE = Charset.forName("UTF-16LE");
179
180    /**
181     * <p>
182     * Eight-bit Unicode Transformation Format.
183     * </p>
184     * <p>
185     * Every implementation of the Java platform is required to support this character encoding.
186     * </p>
187     * 
188     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
189     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
190     */
191    @Deprecated
192    public static final Charset UTF_8 = Charset.forName("UTF-8");
193}