org.apache.juneau.http.Vary Maven / Gradle / Ivy
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package org.apache.juneau.http;
/**
* Represents a parsed Vary HTTP response header.
*
*
* Tells downstream proxies how to match future request headers to decide whether the cached response can be used rather
* than requesting a fresh one from the origin server.
*
*
Example
*
* Vary: *
* Vary: Accept-Language
*
*
* RFC2616 Specification
*
* The Vary field value indicates the set of request-header fields that fully determines, while the response is fresh,
* whether a cache is permitted to use the response to reply to a subsequent request without revalidation.
* For uncacheable or stale responses, the Vary field value advises the user agent about the criteria that were used to
* select the representation.
* A Vary field value of "*" implies that a cache cannot determine from the request headers of a subsequent request
* whether this response is the appropriate representation.
* See section 13.6 for use of the Vary header field by caches.
*
* Vary = "Vary" ":" ( "*" | 1#field-name )
*
*
*
* An HTTP/1.1 server SHOULD include a Vary header field with any cacheable response that is subject to server-driven
* negotiation.
* Doing so allows a cache to properly interpret future requests on that resource and informs the user agent about the
* presence of negotiation on that resource.
* A server MAY include a Vary header field with a non-cacheable response that is subject to server-driven negotiation,
* since this might provide the user agent with useful information about the dimensions over which the response varies
* at the time of the response.
*
*
* A Vary field value consisting of a list of field-names signals that the representation selected for the response is
* based on a selection algorithm which considers ONLY the listed request-header field values in selecting the most
* appropriate representation.
* A cache MAY assume that the same selection will be made for future requests with the same values for the listed
* field names, for the duration of time for which the response is fresh.
*
*
* The field-names given are not limited to the set of standard request-header fields defined by this specification.
* Field names are case-insensitive.
*
*
* A Vary field value of "*" signals that unspecified parameters not limited to the request-headers (e.g., the network
* address of the client), play a role in the selection of the response representation.
* The "*" value MUST NOT be generated by a proxy server; it may only be generated by an origin server.
*
*
Additional Information
*
*/
public final class Vary extends HeaderString {
/**
* Returns a parsed Vary header.
*
* @param value The Vary header string.
* @return The parsed Vary header, or null if the string was null.
*/
public static Vary forString(String value) {
if (value == null)
return null;
return new Vary(value);
}
private Vary(String value) {
super(value);
}
}