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.util.Collections;
021import java.util.SortedMap;
022import java.util.TreeMap;
023
024/**
025 * Charsets required of every implementation of the Java platform.
026 * 
027 * From the Java documentation <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">
028 * Standard charsets</a>:
029 * <p>
030 * <cite>Every implementation of the Java platform is required to support the following character encodings. Consult
031 * the release documentation for your implementation to see if any other encodings are supported. Consult the release
032 * documentation for your implementation to see if any other encodings are supported. </cite>
033 * </p>
034 * 
035 * <ul>
036 * <li><code>US-ASCII</code><br>
037 * Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the Unicode character set.</li>
038 * <li><code>ISO-8859-1</code><br>
039 * ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.</li>
040 * <li><code>UTF-8</code><br>
041 * Eight-bit Unicode Transformation Format.</li>
042 * <li><code>UTF-16BE</code><br>
043 * Sixteen-bit Unicode Transformation Format, big-endian byte order.</li>
044 * <li><code>UTF-16LE</code><br>
045 * Sixteen-bit Unicode Transformation Format, little-endian byte order.</li>
046 * <li><code>UTF-16</code><br>
047 * Sixteen-bit Unicode Transformation Format, byte order specified by a mandatory initial byte-order mark (either order
048 * accepted on input, big-endian used on output.)</li>
049 * </ul>
050 * 
051 * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
052 * @since 2.3
053 * @version $Id: Charsets.java 1686747 2015-06-21 18:44:49Z krosenvold $
054 */
055public class Charsets {
056    //
057    // This class should only contain Charset instances for required encodings. This guarantees that it will load
058    // correctly and without delay on all Java platforms.
059    //
060
061    /**
062     * Constructs a sorted map from canonical charset names to charset objects required of every implementation of the
063     * Java platform.
064     * <p>
065     * From the Java documentation <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">
066     * Standard charsets</a>:
067     * </p>
068     * 
069     * @return An immutable, case-insensitive map from canonical charset names to charset objects.
070     * @see Charset#availableCharsets()
071     * @since 2.5
072     */
073    public static SortedMap<String, Charset> requiredCharsets() {
074        // maybe cache?
075        // TODO Re-implement on Java 7 to use java.nio.charset.StandardCharsets
076        final TreeMap<String, Charset> m = new TreeMap<String, Charset>(String.CASE_INSENSITIVE_ORDER);
077        m.put(ISO_8859_1.name(), ISO_8859_1);
078        m.put(US_ASCII.name(), US_ASCII);
079        m.put(UTF_16.name(), UTF_16);
080        m.put(UTF_16BE.name(), UTF_16BE);
081        m.put(UTF_16LE.name(), UTF_16LE);
082        m.put(UTF_8.name(), UTF_8);
083        return Collections.unmodifiableSortedMap(m);
084    }
085
086    /**
087     * Returns the given Charset or the default Charset if the given Charset is null.
088     * 
089     * @param charset
090     *            A charset or null.
091     * @return the given Charset or the default Charset if the given Charset is null
092     */
093    public static Charset toCharset(final Charset charset) {
094        return charset == null ? Charset.defaultCharset() : charset;
095    }
096
097    /**
098     * Returns a Charset for the named charset. If the name is null, return the default Charset.
099     * 
100     * @param charset
101     *            The name of the requested charset, may be null.
102     * @return a Charset for the named charset
103     * @throws java.nio.charset.UnsupportedCharsetException
104     *             If the named charset is unavailable
105     */
106    public static Charset toCharset(final String charset) {
107        return charset == null ? Charset.defaultCharset() : Charset.forName(charset);
108    }
109
110    /**
111     * CharEncodingISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.
112     * <p>
113     * Every implementation of the Java platform is required to support this character encoding.
114     * </p>
115     * 
116     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
117     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
118     */
119    @Deprecated
120    public static final Charset ISO_8859_1 = Charset.forName("ISO-8859-1");
121
122    /**
123     * <p>
124     * Seven-bit ASCII, also known as ISO646-US, also known as the Basic Latin block of the Unicode character set.
125     * </p>
126     * <p>
127     * Every implementation of the Java platform is required to support this character encoding.
128     * </p>
129     * 
130     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
131     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
132     */
133    @Deprecated
134    public static final Charset US_ASCII = Charset.forName("US-ASCII");
135
136    /**
137     * <p>
138     * Sixteen-bit Unicode Transformation Format, The byte order specified by a mandatory initial byte-order mark
139     * (either order accepted on input, big-endian used on output)
140     * </p>
141     * <p>
142     * Every implementation of the Java platform is required to support this character encoding.
143     * </p>
144     * 
145     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
146     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
147     */
148    @Deprecated
149    public static final Charset UTF_16 = Charset.forName("UTF-16");
150
151    /**
152     * <p>
153     * Sixteen-bit Unicode Transformation Format, big-endian byte order.
154     * </p>
155     * <p>
156     * Every implementation of the Java platform is required to support this character encoding.
157     * </p>
158     * 
159     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
160     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
161     */
162    @Deprecated
163    public static final Charset UTF_16BE = Charset.forName("UTF-16BE");
164
165    /**
166     * <p>
167     * Sixteen-bit Unicode Transformation Format, little-endian byte order.
168     * </p>
169     * <p>
170     * Every implementation of the Java platform is required to support this character encoding.
171     * </p>
172     * 
173     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
174     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
175     */
176    @Deprecated
177    public static final Charset UTF_16LE = Charset.forName("UTF-16LE");
178
179    /**
180     * <p>
181     * Eight-bit Unicode Transformation Format.
182     * </p>
183     * <p>
184     * Every implementation of the Java platform is required to support this character encoding.
185     * </p>
186     * 
187     * @see <a href="http://docs.oracle.com/javase/6/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
188     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
189     */
190    @Deprecated
191    public static final Charset UTF_8 = Charset.forName("UTF-8");
192}