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006// *                                                                                                                         *
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012// ***************************************************************************************************************************
013package org.apache.juneau.http;
014
015import static org.apache.juneau.http.Constants.*;
016
017import org.apache.juneau.internal.*;
018
019
020/**
021 * Represents a parsed <l>Accept-Charset</l> HTTP request header.
022 * 
023 * <p>
024 * Character sets that are acceptable.
025 * 
026 * <h5 class='figure'>Example</h5>
027 * <p class='bcode'>
028 *    Accept-Charset: utf-8
029 * </p>
030 * 
031 * <h5 class='topic'>RFC2616 Specification</h5>
032 * 
033 * The Accept-Charset request-header field can be used to indicate what character sets are acceptable for the response.
034 * 
035 * <p>
036 * This field allows clients capable of understanding more comprehensive or special- purpose character sets to signal
037 * that capability to a server which is capable of representing documents in those character sets.
038 * <p class='bcode'>
039 *    Accept-Charset = "Accept-Charset" ":"
040 *                     1#( ( charset | "*" )[ ";" "q" "=" qvalue ] )
041 * </p>
042 * 
043 * <p>
044 * Character set values are described in section 3.4. Each charset MAY be given an associated quality value which
045 * represents the user's preference for that charset.
046 * The default value is q=1.
047 * An example is...
048 * <p class='bcode'>
049 *    Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
050 * </p>
051 * 
052 * <p>
053 * The special value "*", if present in the Accept-Charset field, matches every character set (including ISO-8859-1)
054 * which is not mentioned elsewhere in the Accept-Charset field.
055 * 
056 * <p>
057 * If no "*" is present in an Accept-Charset field, then all character sets not explicitly mentioned get a quality
058 * value of 0, except for ISO-8859-1, which gets a quality value of 1 if not explicitly mentioned.
059 * 
060 * <p>
061 * If no Accept-Charset header is present, the default is that any character set is acceptable.
062 * 
063 * <p>
064 * If an Accept-Charset header is present, and if the server cannot send a response which is acceptable according to
065 * the Accept-Charset header, then the server SHOULD send an error response with the 406 (not acceptable) status code,
066 * though the sending of an unacceptable response is also allowed.
067 * 
068 * <h5 class='section'>See Also:</h5>
069 * <ul class='doctree'>
070 *    <li class='extlink'><a class='doclink' href='https://www.w3.org/Protocols/rfc2616/rfc2616.html'>Hypertext Transfer Protocol -- HTTP/1.1</a>
071 * </ul>
072 */
073public final class AcceptCharset extends HeaderRangeArray {
074
075   private static final Cache<String,AcceptCharset> cache = new Cache<>(NOCACHE, CACHE_MAX_SIZE);
076
077   /**
078    * Returns a parsed <code>Accept-Charset</code> header.
079    * 
080    * @param value The <code>Accept-Charset</code> header string.
081    * @return The parsed <code>Accept-Charset</code> header, or <jk>null</jk> if the string was null.
082    */
083   public static AcceptCharset forString(String value) {
084      if (value == null)
085         return null;
086      AcceptCharset a = cache.get(value);
087      if (a == null)
088         a = cache.put(value, new AcceptCharset(value));
089      return a;
090   }
091
092   private AcceptCharset(String value) {
093      super(value);
094   }
095}