org.apache.juneau.http.IfMatch Maven / Gradle / Ivy
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package org.apache.juneau.http;
/**
* Represents a parsed If-Match HTTP request header.
*
*
* Only perform the action if the client supplied entity matches the same entity on the server.
* This is mainly for methods like PUT to only update a resource if it has not been modified since the user last
* updated it.
*
*
Example
*
* If-Match: "737060cd8c284d8af7ad3082f209582d"
*
*
* RFC2616 Specification
*
* The If-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 one of those entities
* is current by including a list of their associated entity tags in the If-Match header field.
* Entity tags are defined in section 3.11.
* The purpose of this feature is to allow efficient updates of cached information with a minimum amount of transaction
* overhead.
* It is also used, on updating requests, to prevent inadvertent modification of the wrong version of a resource.
* As a special case, the value "*" matches any current entity of the resource.
*
*
* If-Match = "If-Match" ":" ( "*" | 1#entity-tag )
*
*
*
* 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-Match header) on that resource, or if "*" is given and any current entity exists
* for that resource, then the server MAY perform the requested method as if the If-Match header field did not exist.
*
*
* A server MUST use the strong comparison function (see section 13.3.3) to compare the entity tags in If-Match.
*
*
* If none of the entity tags match, or if "*" is given and no current entity exists, the server MUST NOT perform the
* requested method, and MUST return a 412 (Precondition Failed) response.
* This behavior is most useful when the client wants to prevent an updating method, such as PUT, from modifying a
* resource that has changed since the client last retrieved it.
*
*
* If the request would, without the If-Match header field, result in anything other than a 2xx or 412 status, then the
* If-Match header MUST be ignored.
*
*
* The meaning of "If-Match: *" is that the method SHOULD 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 MUST NOT be performed if the
* representation does not exist.
*
*
* A request intended to update a resource (e.g., a PUT) MAY include an If-Match header field to signal that the request
* method MUST NOT be applied if the entity corresponding to the If-Match value (a single entity tag) is no longer a
* representation of that resource.
* This allows the user to indicate that they do not wish the request to be successful if the resource has been changed
* without their knowledge.
*
*
* Examples:
*
* If-Match: "xyzzy"
* If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
* If-Match: *
*
*
*
* The result of a request having both an If-Match header field and either an If-None-Match or an If-Modified-Since
* header fields is undefined by this specification.
*
*
Additional Information
*
*/
public final class IfMatch extends HeaderEntityValidatorArray {
/**
* Returns a parsed If-Match header.
*
* @param value The If-Match header string.
* @return The parsed If-Match header, or null if the string was null.
*/
public static IfMatch forString(String value) {
if (value == null)
return null;
return new IfMatch(value);
}
private IfMatch(String value) {
super(value);
}
}