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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; 014 015/** 016 * Represents a parsed <l>Cache-Control</l> HTTP request header. 017 * 018 * <p> 019 * Used to specify directives that must be obeyed by all caching mechanisms along the request-response chain. 020 * 021 * <h5 class='figure'>Example</h5> 022 * <p class='bcode'> 023 * Cache-Control: no-cache 024 * </p> 025 * 026 * <h5 class='topic'>RFC2616 Specification</h5> 027 * 028 * The Cache-Control general-header field is used to specify directives that MUST be obeyed by all caching mechanisms 029 * along the request/response chain. 030 * The directives specify behavior intended to prevent caches from adversely interfering with the request or response. 031 * These directives typically override the default caching algorithms. 032 * Cache directives are unidirectional in that the presence of a directive in a request does not imply that the same 033 * directive is to be given in the response. 034 * 035 * <p> 036 * Note that HTTP/1.0 caches might not implement Cache-Control and might only implement Pragma: no-cache (see section 037 * 14.32). 038 * 039 * <p> 040 * Cache directives MUST be passed through by a proxy or gateway application, regardless of their significance to that 041 * application, since the directives might be applicable to all recipients along the request/response chain. 042 * It is not possible to specify a cache- directive for a specific cache. 043 * 044 * <p class='bcode'> 045 * Cache-Control = "Cache-Control" ":" 1#cache-directive 046 * cache-directive = cache-request-directive 047 * | cache-response-directive 048 * cache-request-directive = 049 * "no-cache" ; Section 14.9.1 050 * | "no-store" ; Section 14.9.2 051 * | "max-age" "=" delta-seconds ; Section 14.9.3, 14.9.4 052 * | "max-stale" [ "=" delta-seconds ] ; Section 14.9.3 053 * | "min-fresh" "=" delta-seconds ; Section 14.9.3 054 * | "no-transform" ; Section 14.9.5 055 * | "only-if-cached" ; Section 14.9.4 056 * | cache-extension ; Section 14.9.6 057 * cache-response-directive = 058 * "public" ; Section 14.9.1 059 * | "private" [ "=" <"> 1#field-name <"> ] ; Section 14.9.1 060 * | "no-cache" [ "=" <"> 1#field-name <"> ]; Section 14.9.1 061 * | "no-store" ; Section 14.9.2 062 * | "no-transform" ; Section 14.9.5 063 * | "must-revalidate" ; Section 14.9.4 064 * | "proxy-revalidate" ; Section 14.9.4 065 * | "max-age" "=" delta-seconds ; Section 14.9.3 066 * | "s-maxage" "=" delta-seconds ; Section 14.9.3 067 * | cache-extension ; Section 14.9.6 068 * cache-extension = token [ "=" ( token | quoted-string ) ] 069 * </p> 070 * 071 * <p> 072 * When a directive appears without any 1#field-name parameter, the directive applies to the entire request or response. 073 * When such a directive appears with a 1#field-name parameter, it applies only to the named field or fields, and not 074 * to the rest of the request or response. This mechanism supports extensibility; implementations of future versions 075 * of the HTTP protocol might apply these directives to header fields not defined in HTTP/1.1. 076 * 077 * <p> 078 * The cache-control directives can be broken down into these general categories: 079 * <ul> 080 * <li>Restrictions on what are cacheable; these may only be imposed by the origin server. 081 * <li>Restrictions on what may be stored by a cache; these may be imposed by either the origin server or the user 082 * agent. 083 * <li>Modifications of the basic expiration mechanism; these may be imposed by either the origin server or the 084 * user agent. 085 * <li>Controls over cache revalidation and reload; these may only be imposed by a user agent. 086 * <li>Control over transformation of entities. 087 * <li>Extensions to the caching system. 088 * </ul> 089 * 090 * <h5 class='section'>See Also:</h5> 091 * <ul class='doctree'> 092 * <li class='extlink'><a class='doclink' href='https://www.w3.org/Protocols/rfc2616/rfc2616.html'>Hypertext Transfer Protocol -- HTTP/1.1</a> 093 * </ul> 094 */ 095public final class CacheControl extends HeaderString { 096 097 /** 098 * Returns a parsed <code>Cache-Control</code> header. 099 * 100 * @param value The <code>Cache-Control</code> header string. 101 * @return The parsed <code>Cache-Control</code> header, or <jk>null</jk> if the string was null. 102 */ 103 public static CacheControl forString(String value) { 104 if (value == null) 105 return null; 106 return new CacheControl(value); 107 } 108 109 private CacheControl(String value) { 110 super(value); 111 } 112}