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HeaderMap.java
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55 lines (52 loc) · 2.47 KB
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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 {
}