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.StandardCharsets;
021import java.nio.charset.UnsupportedCharsetException;
022import java.util.Collections;
023import java.util.SortedMap;
024import java.util.TreeMap;
025
026/**
027 * Charsets required of every implementation of the Java platform.
028 *
029 * From the Java documentation <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">
030 * Standard charsets</a>:
031 * <p>
032 * <cite>Every implementation of the Java platform is required to support the following character encodings. Consult
033 * the release documentation for your implementation to see if any other encodings are supported. Consult the release
034 * documentation for your implementation to see if any other encodings are supported. </cite>
035 * </p>
036 *
037 * <ul>
038 * <li>{@code US-ASCII}<br>
039 * Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the Basic Latin block of the Unicode character set.</li>
040 * <li>{@code ISO-8859-1}<br>
041 * ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.</li>
042 * <li>{@code UTF-8}<br>
043 * Eight-bit Unicode Transformation Format.</li>
044 * <li>{@code UTF-16BE}<br>
045 * Sixteen-bit Unicode Transformation Format, big-endian byte order.</li>
046 * <li>{@code UTF-16LE}<br>
047 * Sixteen-bit Unicode Transformation Format, little-endian byte order.</li>
048 * <li>{@code UTF-16}<br>
049 * Sixteen-bit Unicode Transformation Format, byte order specified by a mandatory initial byte-order mark (either order
050 * accepted on input, big-endian used on output.)</li>
051 * </ul>
052 *
053 * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
054 * @since 2.3
055 */
056public class Charsets {
057
058    //
059    // This class should only contain Charset instances for required encodings. This guarantees that it will load
060    // correctly and without delay on all Java platforms.
061    //
062
063    private static final SortedMap<String, Charset> STANDARD_CHARSET_MAP;
064
065    static {
066        final SortedMap<String, Charset> standardCharsetMap = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
067        standardCharsetMap.put(StandardCharsets.ISO_8859_1.name(), StandardCharsets.ISO_8859_1);
068        standardCharsetMap.put(StandardCharsets.US_ASCII.name(), StandardCharsets.US_ASCII);
069        standardCharsetMap.put(StandardCharsets.UTF_16.name(), StandardCharsets.UTF_16);
070        standardCharsetMap.put(StandardCharsets.UTF_16BE.name(), StandardCharsets.UTF_16BE);
071        standardCharsetMap.put(StandardCharsets.UTF_16LE.name(), StandardCharsets.UTF_16LE);
072        standardCharsetMap.put(StandardCharsets.UTF_8.name(), StandardCharsets.UTF_8);
073        STANDARD_CHARSET_MAP = Collections.unmodifiableSortedMap(standardCharsetMap);
074    }
075
076    /**
077     * Constructs a sorted map from canonical charset names to charset objects required of every implementation of the
078     * Java platform.
079     * <p>
080     * From the Java documentation <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">
081     * Standard charsets</a>:
082     * </p>
083     *
084     * @return An immutable, case-insensitive map from canonical charset names to charset objects.
085     * @see Charset#availableCharsets()
086     * @since 2.5
087     */
088    public static SortedMap<String, Charset> requiredCharsets() {
089        return STANDARD_CHARSET_MAP;
090    }
091
092    /**
093     * Returns the given Charset or the default Charset if the given Charset is null.
094     *
095     * @param charset
096     *            A charset or null.
097     * @return the given Charset or the default Charset if the given Charset is null
098     */
099    public static Charset toCharset(final Charset charset) {
100        return charset == null ? Charset.defaultCharset() : charset;
101    }
102
103    /**
104     * Returns a Charset for the named charset. If the name is null, return the default Charset.
105     *
106     * @param charsetName The name of the requested charset, may be null.
107     * @return a Charset for the named charset.
108     * @throws UnsupportedCharsetException If the named charset is unavailable (unchecked exception).
109     */
110    public static Charset toCharset(final String charsetName) throws UnsupportedCharsetException {
111        return charsetName == null ? Charset.defaultCharset() : Charset.forName(charsetName);
112    }
113
114    /**
115     * CharEncodingISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1.
116     * <p>
117     * Every implementation of the Java platform is required to support this character encoding.
118     * </p>
119     *
120     * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
121     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
122     */
123    @Deprecated
124    public static final Charset ISO_8859_1 = StandardCharsets.ISO_8859_1;
125
126    /**
127     * <p>
128     * Seven-bit ASCII, also known as ISO646-US, also known as the Basic Latin block of the Unicode character set.
129     * </p>
130     * <p>
131     * Every implementation of the Java platform is required to support this character encoding.
132     * </p>
133     *
134     * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
135     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
136     */
137    @Deprecated
138    public static final Charset US_ASCII = StandardCharsets.US_ASCII;
139
140    /**
141     * <p>
142     * Sixteen-bit Unicode Transformation Format, The byte order specified by a mandatory initial byte-order mark
143     * (either order accepted on input, big-endian used on output)
144     * </p>
145     * <p>
146     * Every implementation of the Java platform is required to support this character encoding.
147     * </p>
148     *
149     * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
150     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
151     */
152    @Deprecated
153    public static final Charset UTF_16 = StandardCharsets.UTF_16;
154
155    /**
156     * <p>
157     * Sixteen-bit Unicode Transformation Format, big-endian byte order.
158     * </p>
159     * <p>
160     * Every implementation of the Java platform is required to support this character encoding.
161     * </p>
162     *
163     * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
164     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
165     */
166    @Deprecated
167    public static final Charset UTF_16BE = StandardCharsets.UTF_16BE;
168
169    /**
170     * <p>
171     * Sixteen-bit Unicode Transformation Format, little-endian byte order.
172     * </p>
173     * <p>
174     * Every implementation of the Java platform is required to support this character encoding.
175     * </p>
176     *
177     * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
178     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
179     */
180    @Deprecated
181    public static final Charset UTF_16LE = StandardCharsets.UTF_16LE;
182
183    /**
184     * <p>
185     * Eight-bit Unicode Transformation Format.
186     * </p>
187     * <p>
188     * Every implementation of the Java platform is required to support this character encoding.
189     * </p>
190     *
191     * @see <a href="https://docs.oracle.com/javase/7/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
192     * @deprecated Use Java 7's {@link java.nio.charset.StandardCharsets}
193     */
194    @Deprecated
195    public static final Charset UTF_8 = StandardCharsets.UTF_8;
196}