org.apache.juneau.http.Expires Maven / Gradle / Ivy
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package org.apache.juneau.http;
import org.apache.juneau.http.annotation.*;
/**
* Represents a parsed Expires HTTP response header.
*
*
* Gives the date/time after which the response is considered stale (in "HTTP-date" format as defined by RFC 7231).
*
*
Example
*
* Expires: Thu, 01 Dec 1994 16:00:00 GMT
*
*
* RFC2616 Specification
*
* The Expires entity-header field gives the date/time after which the response is considered stale.
* A stale cache entry may not normally be returned by a cache (either a proxy cache or a user agent cache) unless it is
* first validated with the origin server
* (or with an intermediate cache that has a fresh copy of the entity).
* See section 13.2 for further discussion of the expiration model.
*
*
* The presence of an Expires field does not imply that the original resource will change or cease to exist at, before,
* or after that time.
*
*
* The format is an absolute date and time as defined by HTTP-date in section 3.3.1; it MUST be in RFC 1123 date format:
*
*
* Expires = "Expires" ":" HTTP-date
*
*
*
* An example of its use is...
*
* Expires: Thu, 01 Dec 1994 16:00:00 GMT
*
*
*
* Note: if a response includes a Cache-Control field with the max-age directive (see section 14.9.3), that directive
* overrides the Expires field.
*
*
* HTTP/1.1 clients and caches MUST treat other invalid date formats, especially including the value "0", as in the past
* (i.e., "already expired").
*
*
* To mark a response as "already expired," an origin server sends an Expires date that is equal to the Date header
* value.
* (See the rules for expiration calculations in section 13.2.4.)
*
*
* To mark a response as "never expires," an origin server sends an Expires date approximately one year from the time
* the response is sent.
* HTTP/1.1 servers SHOULD NOT send Expires dates more than one year in the future.
*
*
* The presence of an Expires header field with a date value of some time in the future on a response that otherwise
* would by default be non-cacheable indicates that the response is cacheable, unless indicated otherwise by a
* Cache-Control header field (section 14.9).
*
*
See Also:
*
* - {@doc RFC2616}
*
*/
@Header("Expires")
public final class Expires extends HeaderDate {
/**
* Returns a parsed Expires header.
*
* @param value The Expires header string.
* @return The parsed Expires header, or null if the string was null.
*/
public static Expires forString(String value) {
if (value == null)
return null;
return new Expires(value);
}
private Expires(String value) {
super(value);
}
}