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See the License for the * 011// * specific language governing permissions and limitations under the License. * 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 * Represents a parsed <l>Accept-Language</l> HTTP request header. 022 * 023 * <p> 024 * List of acceptable human languages for response. 025 * 026 * <h5 class='figure'>Example</h5> 027 * <p class='bcode w800'> 028 * Accept-Language: en-US 029 * </p> 030 * 031 * <h5 class='topic'>RFC2616 Specification</h5> 032 * 033 * The Accept-Language request-header field is similar to Accept, but restricts the set of natural languages that are 034 * preferred as a response to the request. 035 * Language tags are defined in section 3.10. 036 * 037 * <p class='bcode w800'> 038 * Accept-Language = "Accept-Language" ":" 039 * 1#( language-range [ ";" "q" "=" qvalue ] ) 040 * language-range = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" ) 041 * </p> 042 * 043 * <p> 044 * Each language-range MAY be given an associated quality value which represents an estimate of the user's preference 045 * for the languages specified by that range. 046 * The quality value defaults to "q=1". 047 * For example... 048 * <p class='bcode w800'> 049 * Accept-Language: da, en-gb;q=0.8, en;q=0.7 050 * </p> 051 * <p> 052 * ...would mean: "I prefer Danish, but will accept British English and other types of English." 053 * 054 * <p> 055 * A language-range matches a language-tag if it exactly equals the tag, or if it exactly equals a prefix of the tag 056 * such that the first tag character following the prefix is "-". 057 * 058 * <p> 059 * The special range "*", if present in the Accept-Language field, matches every tag not matched by any other range 060 * present in the Accept-Language field. 061 * 062 * <p> 063 * Note: This use of a prefix matching rule does not imply that language tags are assigned to languages in such a way 064 * that it is always true that if a user understands a language with a certain 065 * tag, then this user will also understand all languages with tags for which this tag is a prefix. 066 * The prefix rule simply allows the use of prefix tags if this is the case. 067 * 068 * <p> 069 * The language quality factor assigned to a language-tag by the Accept-Language field is the quality value of the 070 * longest language- range in the field that matches the language-tag. 071 * 072 * <p> 073 * If no language- range in the field matches the tag, the language quality factor assigned is 0. 074 * 075 * <p> 076 * If no Accept-Language header is present in the request, the server SHOULD assume that all languages are equally 077 * acceptable. 078 * 079 * <p> 080 * If an Accept-Language header is present, then all languages which are assigned a quality factor greater than 0 are 081 * acceptable. 082 * 083 * <p> 084 * It might be contrary to the privacy expectations of the user to send an Accept-Language header with the complete 085 * linguistic preferences of the user in every request. 086 * For a discussion of this issue, see section 15.1.4. 087 * 088 * <p> 089 * As intelligibility is highly dependent on the individual user, it is recommended that client applications make the 090 * choice of linguistic preference available to the user. 091 * If the choice is not made available, then the Accept-Language header field MUST NOT be given in the request. 092 * 093 * <p> 094 * Note: When making the choice of linguistic preference available to the user, we remind implementors of the fact that 095 * users are not familiar with the details of language matching as described above, and should provide appropriate 096 * guidance. 097 * As an example, users might assume that on selecting "en-gb", they will be served any kind of English document if 098 * British English is not available. 099 * A user agent might suggest in such a case to add "en" to get the best matching behavior. 100 * 101 * <ul class='seealso'> 102 * <li class='extlink'>{@doc RFC2616} 103 * </ul> 104 */ 105@Header("Accept-Language") 106public final class AcceptLanguage extends HeaderRangeArray { 107 108 private static final Cache<String,AcceptLanguage> cache = new Cache<>(NOCACHE, CACHE_MAX_SIZE); 109 110 /** 111 * Returns a parsed <c>Accept-Language</c> header. 112 * 113 * @param value The <c>Accept-Language</c> header string. 114 * @return The parsed <c>Accept-Language</c> header, or <jk>null</jk> if the string was null. 115 */ 116 public static AcceptLanguage forString(String value) { 117 if (value == null) 118 return null; 119 AcceptLanguage a = cache.get(value); 120 if (a == null) 121 a = cache.put(value, new AcceptLanguage(value)); 122 return a; 123 } 124 125 private AcceptLanguage(String raw) { 126 super(raw); 127 } 128}