| // *************************************************************************************************************************** |
| // * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file * |
| // * distributed with this work for additional information regarding copyright ownership. The ASF licenses this file * |
| // * to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance * |
| // * with the License. You may obtain a copy of the License at * |
| // * * |
| // * http://www.apache.org/licenses/LICENSE-2.0 * |
| // * * |
| // * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an * |
| // * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the * |
| // * specific language governing permissions and limitations under the License. * |
| // *************************************************************************************************************************** |
| package org.apache.juneau.http; |
| |
| import org.apache.juneau.http.annotation.*; |
| |
| /** |
| * Represents a parsed <l>If-None-Match</l> HTTP request header. |
| * |
| * <p> |
| * Allows a 304 Not Modified to be returned if content is unchanged. |
| * |
| * <h5 class='figure'>Example</h5> |
| * <p class='bcode w800'> |
| * If-None-Match: "737060cd8c284d8af7ad3082f209582d" |
| * </p> |
| * |
| * <h5 class='topic'>RFC2616 Specification</h5> |
| * |
| * The If-None-Match request-header field is used with a method to make it conditional. |
| * A client that has one or more entities previously obtained from the resource can verify that none of those entities |
| * is current by including a list of their associated entity tags in the If-None-Match header field. |
| * The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction |
| * overhead. |
| * It is also used to prevent a method (e.g. PUT) from inadvertently modifying an existing resource when the client |
| * believes that the resource does not exist. |
| * |
| * <p> |
| * As a special case, the value "*" matches any current entity of the resource. |
| * |
| * <p class='bcode w800'> |
| * If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag ) |
| * </p> |
| * |
| * <p> |
| * If any of the entity tags match the entity tag of the entity that would have been returned in the response to a |
| * similar GET request (without the If-None-Match header) on that resource, or if "*" is given |
| * and any current entity exists for that resource, then the server MUST NOT perform the requested method, unless |
| * required to do so because the resource's modification date fails to match that supplied in an If-Modified-Since |
| * header field in the request. |
| * Instead, if the request method was GET or HEAD, the server SHOULD respond with a 304 (Not Modified) response, |
| * including the cache- related header fields (particularly ETag) of one of the entities that matched. |
| * For all other request methods, the server MUST respond with a status of 412 (Precondition Failed). |
| * |
| * <p> |
| * See section 13.3.3 for rules on how to determine if two entities tags match. |
| * The weak comparison function can only be used with GET or HEAD requests. |
| * |
| * <p> |
| * If none of the entity tags match, then the server MAY perform the requested method as if the If-None-Match header |
| * field did not exist, but MUST also ignore any If-Modified-Since header field(s) in the request. |
| * That is, if no entity tags match, then the server MUST NOT return a 304 (Not Modified) response. |
| * |
| * <p> |
| * If the request would, without the If-None-Match header field, result in anything other than a 2xx or 304 status, |
| * then the If-None-Match header MUST be ignored. |
| * (See section 13.3.4 for a discussion of server behavior when both If-Modified-Since and If-None-Match appear in the |
| * same request.) |
| * |
| * <p> |
| * The meaning of "If-None-Match: *" is that the method MUST NOT be performed if the representation selected by the |
| * origin server (or by a cache, possibly using the Vary mechanism, see section 14.44) exists, and SHOULD be performed |
| * if the representation does not exist. |
| * This feature is intended to be useful in preventing races between PUT operations. |
| * |
| * <p> |
| * Examples: |
| * <p class='bcode w800'> |
| * If-None-Match: "xyzzy" |
| * If-None-Match: W/"xyzzy" |
| * If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz" |
| * If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz" |
| * If-None-Match: * |
| * </p> |
| * |
| * <p> |
| * The result of a request having both an If-None-Match header field and either an If-Match or an If-Unmodified-Since |
| * header fields is undefined by this specification. |
| * |
| * <ul class='seealso'> |
| * <li class='extlink'>{@doc RFC2616} |
| * </ul> |
| */ |
| @Header("If-None-Match") |
| public final class IfNoneMatch extends HeaderEntityValidatorArray { |
| |
| /** |
| * Returns a parsed <c>If-None-Match</c> header. |
| * |
| * @param value The <c>If-None-Match</c> header string. |
| * @return The parsed <c>If-None-Match</c> header, or <jk>null</jk> if the string was null. |
| */ |
| public static IfNoneMatch forString(String value) { |
| if (value == null) |
| return null; |
| return new IfNoneMatch(value); |
| } |
| |
| private IfNoneMatch(String value) { |
| super(value); |
| } |
| } |