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There is a newer version: 13.5
/**
 * Copyright 2012-2019 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.codec;

import java.lang.reflect.Type;
import feign.RequestTemplate;
import feign.Util;
import static java.lang.String.format;

/**
 * Encodes an object into an HTTP request body. Like {@code javax.websocket.Encoder}. {@code
 * Encoder} is used when a method parameter has no {@code @Param} annotation. For example: 

 * 
 * 
 * 
 * @POST
 * @Path("/")
 * void create(User user);
 * 
 * 
 * Example implementation: 

 * 
 * 
 * 
 * public class GsonEncoder implements Encoder {
 *   private final Gson gson;
 *
 *   public GsonEncoder(Gson gson) {
 *     this.gson = gson;
 *   }
 *
 *   @Override
 *   public void encode(Object object, Type bodyType, RequestTemplate template) {
 *     template.body(gson.toJson(object, bodyType));
 *   }
 * }
 * 
 *
 * 
 * 
Form encoding
 * 
 * If any parameters are found in {@link feign.MethodMetadata#formParams()}, they will be collected
 * and passed to the Encoder as a map.
 *
 * 

 * Ex. The following is a form. Notice the parameters aren't consumed in the request line. A map
 * including "username" and "password" keys will passed to the encoder, and the body type will be
 * {@link #MAP_STRING_WILDCARD}.
 * 
 * 
 * @RequestLine("POST /")
 * Session login(@Param("username") String username, @Param("password") String password);
 * 
 */
public interface Encoder {
  /** Type literal for {@code Map}, indicating the object to encode is a form. */
  Type MAP_STRING_WILDCARD = Util.MAP_STRING_WILDCARD;

  /**
   * Converts objects to an appropriate representation in the template.
   *
   * @param object what to encode as the request body.
   * @param bodyType the type the object should be encoded as. {@link #MAP_STRING_WILDCARD}
   *        indicates form encoding.
   * @param template the request template to populate.
   * @throws EncodeException when encoding failed due to a checked exception.
   */
  void encode(Object object, Type bodyType, RequestTemplate template) throws EncodeException;

  /**
   * Default implementation of {@code Encoder}.
   */
  class Default implements Encoder {

    @Override
    public void encode(Object object, Type bodyType, RequestTemplate template) {
      if (bodyType == String.class) {
        template.body(object.toString());
      } else if (bodyType == byte[].class) {
        template.body((byte[]) object, null);
      } else if (object != null) {
        throw new EncodeException(
            format("%s is not a type supported by this encoder.", object.getClass()));
      }
    }
  }
}