| // *************************************************************************************************************************** |
| // * 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-Modified-Since</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-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
| * </p> |
| * |
| * <h5 class='topic'>RFC2616 Specification</h5> |
| * |
| * The If-Modified-Since request-header field is used with a method to make it conditional: |
| * if the requested variant has not been modified since the time specified in this field, an entity will not be returned |
| * from the server; instead, a 304 (not modified) response will be returned without any message-body. |
| * |
| * <p class='bcode w800'> |
| * If-Modified-Since = "If-Modified-Since" ":" HTTP-date |
| * </p> |
| * |
| * <p> |
| * An example of the field is: |
| * <p class='bcode w800'> |
| * If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT |
| * </p> |
| * |
| * <p> |
| * A GET method with an If-Modified-Since header and no Range header requests that the identified entity be transferred |
| * only if it has been modified since the date given by the If-Modified-Since header. |
| * The algorithm for determining this includes the following cases: |
| * <ol> |
| * <li>If the request would normally result in anything other than a 200 (OK) status, or if the passed |
| * If-Modified-Since date is invalid, the response is exactly the same as for a normal GET. |
| * A date which is later than the server's current time is invalid. |
| * <li>If the variant has been modified since the If-Modified-Since date, the response is exactly the same as for a |
| * normal GET. |
| * <li>If the variant has not been modified since a valid If-Modified-Since date, the server SHOULD return a 304 |
| * (Not Modified) response. |
| * </ol> |
| * |
| * <p> |
| * The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction |
| * overhead. |
| * |
| * <p> |
| * Note: The Range request-header field modifies the meaning of If-Modified-Since; see section 14.35 for full details. |
| * |
| * <p> |
| * Note: If-Modified-Since times are interpreted by the server, whose clock might not be synchronized with the client. |
| * |
| * <p> |
| * Note: When handling an If-Modified-Since header field, some servers will use an exact date comparison function, |
| * rather than a less-than function, for deciding whether to send a 304 (Not Modified) response. |
| * To get best results when sending an If-Modified-Since header field for cache validation, clients are |
| * advised to use the exact date string received in a previous Last-Modified header field whenever possible. |
| * |
| * <p> |
| * Note: If a client uses an arbitrary date in the If-Modified-Since header instead of a date taken from the |
| * Last-Modified header for the same request, the client should be aware of the fact that this date is interpreted in |
| * the server's understanding of time. |
| * The client should consider unsynchronized clocks and rounding problems due to the different encodings of time between |
| * the client and server. |
| * This includes the possibility of race conditions if the document has changed between the time it was first requested |
| * and the If-Modified-Since date of a subsequent request, and the possibility of clock-skew-related problems if the |
| * If-Modified-Since date is derived from the client's clock without correction to the server's clock. |
| * Corrections for different time bases between client and server are at best approximate due to network latency. |
| * The result of a request having both an If-Modified-Since 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-Modified-Since") |
| public final class IfModifiedSince extends HeaderDate { |
| |
| /** |
| * Returns a parsed <c>If-Modified-Since</c> header. |
| * |
| * @param value The <c>If-Modified-Since</c> header string. |
| * @return The parsed <c>If-Modified-Since</c> header, or <jk>null</jk> if the string was null. |
| */ |
| public static IfModifiedSince forString(String value) { |
| if (value == null) |
| return null; |
| return new IfModifiedSince(value); |
| } |
| |
| private IfModifiedSince(String value) { |
| super(value); |
| } |
| } |