001// ***************************************************************************************************************************
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006// *                                                                                                                         *
007// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
008// *                                                                                                                         *
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012// ***************************************************************************************************************************
013package org.apache.juneau.http;
014
015import static org.apache.juneau.http.Constants.*;
016
017import org.apache.juneau.http.annotation.*;
018import org.apache.juneau.internal.*;
019
020
021/**
022 * Represents a parsed <l>Accept-Charset</l> HTTP request header.
023 *
024 * <p>
025 * Character sets that are acceptable.
026 *
027 * <h5 class='figure'>Example</h5>
028 * <p class='bcode w800'>
029 *    Accept-Charset: utf-8
030 * </p>
031 *
032 * <h5 class='topic'>RFC2616 Specification</h5>
033 *
034 * The Accept-Charset request-header field can be used to indicate what character sets are acceptable for the response.
035 *
036 * <p>
037 * This field allows clients capable of understanding more comprehensive or special- purpose character sets to signal
038 * that capability to a server which is capable of representing documents in those character sets.
039 * <p class='bcode w800'>
040 *    Accept-Charset = "Accept-Charset" ":"
041 *                     1#( ( charset | "*" )[ ";" "q" "=" qvalue ] )
042 * </p>
043 *
044 * <p>
045 * Character set values are described in section 3.4. Each charset MAY be given an associated quality value which
046 * represents the user's preference for that charset.
047 * The default value is q=1.
048 * An example is...
049 * <p class='bcode w800'>
050 *    Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
051 * </p>
052 *
053 * <p>
054 * The special value "*", if present in the Accept-Charset field, matches every character set (including ISO-8859-1)
055 * which is not mentioned elsewhere in the Accept-Charset field.
056 *
057 * <p>
058 * If no "*" is present in an Accept-Charset field, then all character sets not explicitly mentioned get a quality
059 * value of 0, except for ISO-8859-1, which gets a quality value of 1 if not explicitly mentioned.
060 *
061 * <p>
062 * If no Accept-Charset header is present, the default is that any character set is acceptable.
063 *
064 * <p>
065 * If an Accept-Charset header is present, and if the server cannot send a response which is acceptable according to
066 * the Accept-Charset header, then the server SHOULD send an error response with the 406 (not acceptable) status code,
067 * though the sending of an unacceptable response is also allowed.
068 *
069 * <ul class='seealso'>
070 *    <li class='extlink'>{@doc RFC2616}
071 * </ul>
072 */
073@Header("Accept-Charset")
074public final class AcceptCharset extends HeaderRangeArray {
075
076   private static final Cache<String,AcceptCharset> cache = new Cache<>(NOCACHE, CACHE_MAX_SIZE);
077
078   /**
079    * Returns a parsed <c>Accept-Charset</c> header.
080    *
081    * @param value The <c>Accept-Charset</c> header string.
082    * @return The parsed <c>Accept-Charset</c> header, or <jk>null</jk> if the string was null.
083    */
084   public static AcceptCharset forString(String value) {
085      if (value == null)
086         return null;
087      AcceptCharset a = cache.get(value);
088      if (a == null)
089         a = cache.put(value, new AcceptCharset(value));
090      return a;
091   }
092
093   private AcceptCharset(String value) {
094      super(value);
095   }
096}