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/**
* Copyright 2012-2018 The Feign Authors
*
* Licensed 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 feign;
import java.lang.annotation.Retention;
import java.util.List;
import java.util.Map;
import static java.lang.annotation.ElementType.PARAMETER;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
/**
* A template parameter that can be applied to a Map that contains header entries, where the keys
* are Strings that are the header field names and the values are the header field values. The
* headers specified by the map will be applied to the request after all other processing, and will
* take precedence over any previously specified header parameters. <br>
* This parameter is useful in cases where different header fields and values need to be set on an
* API method on a per-request basis in a thread-safe manner and independently of Feign client
* construction. A concrete example of a case like this are custom metadata header fields (e.g. as
* "x-amz-meta-*" or "x-goog-meta-*") where the header field names are dynamic and the range of keys
* cannot be determined a priori. The {@link Headers} annotation does not allow this because the
* header fields that it defines are static (it is not possible to add or remove fields on a
* per-request basis), and doing this using a custom {@link Target} or {@link RequestInterceptor}
* can be cumbersome (it requires more code for per-method customization, it is difficult to
* implement in a thread-safe manner and it requires customization when the Feign client for the API
* is built). <br>
*
* <pre>
* ...
* @RequestLine("GET /servers/{serverId}")
* void get(@Param("serverId") String serverId, @HeaderMap Map<String, Object>);
* ...
* </pre>
*
* The annotated parameter must be an instance of {@link Map}, and the keys must be Strings. The
* header field value of a key will be the value of its toString method, except in the following
* cases: <br>
* <br>
* <ul>
* <li>if the value is null, the value will remain null (rather than converting to the String
* "null")
* <li>if the value is an {@link Iterable}, it is converted to a {@link List} of String objects
* where each value in the list is either null if the original value was null or the value's
* toString representation otherwise.
* </ul>
* <br>
* Once this conversion is applied, the query keys and resulting String values follow the same
* contract as if they were set using {@link RequestTemplate#header(String, String...)}.
*/
@Retention(RUNTIME)
@java.lang.annotation.Target(PARAMETER)
public @interface HeaderMap {
}