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This module overrides OpenFeign/feign annotation processing to instead use standard ones supplied by the spring annotations specification.
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/**
 * Copyright (C) 2017 Marvin Herman Froeder ([email protected])
 *
 * 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.spring;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collection;

import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import feign.Contract.BaseContract;
import feign.MethodMetadata;

public class SpringContract extends BaseContract {

    static final String ACCEPT = "Accept";
    static final String CONTENT_TYPE = "Content-Type";

    protected void processAnnotationOnClass(MethodMetadata data, Class targetType) {
        if (targetType.isAnnotationPresent(RequestMapping.class)) {
            RequestMapping requestMapping = targetType.getAnnotation(RequestMapping.class);
            appendMappings(data, requestMapping.value());

            if (requestMapping.method().length == 1)
                data.template().method(requestMapping.method()[0].name());

            handleProducesAnnotation(data, requestMapping.produces());
            handleConsumesAnnotation(data, requestMapping.consumes());

        }
    }

    private void appendMappings(MethodMetadata data, String[] mappings) {
        for (int i = 0; i < mappings.length; i++) {
            String mapping = mappings[i];
            if (data.template().url().length() != 0 && !data.template().url().endsWith("/") && !mapping.startsWith("/"))
                data.template().append("/");

            data.template().append(mapping);
        }
    }

    @Override
    protected void processAnnotationOnMethod(MethodMetadata data, Annotation annotation, Method method) {
        if (annotation.annotationType() == RequestMapping.class) {
            RequestMapping requestMapping = RequestMapping.class.cast(annotation);
            String[] mappings = requestMapping.value();
            appendMappings(data, mappings);

            if (requestMapping.method().length == 1)
                data.template().method(requestMapping.method()[0].name());

        }

        if (annotation.annotationType() == ResponseBody.class)
            handleConsumesAnnotation(data, "application/json");

        if (annotation.annotationType() == ExceptionHandler.class)
            data.template().method("CONFIG");
    }

    private void handleProducesAnnotation(MethodMetadata data, String... produces) {
        if (produces.length == 0)
            return;
        data.template().header(ACCEPT, (String) null); // remove any previous
                                                       // produces
        data.template().header(ACCEPT, produces[0]);
    }

    private void handleConsumesAnnotation(MethodMetadata data, String... consumes) {
        if (consumes.length == 0)
            return;
        data.template().header(CONTENT_TYPE, (String) null); // remove any previous
                                                             // consumes
        data.template().header(CONTENT_TYPE, consumes[0]);
    }

    @Override
    protected boolean processAnnotationsOnParameter(MethodMetadata data, Annotation[] annotations, int paramIndex) {
        boolean isHttpParam = false;
        for (Annotation parameterAnnotation : annotations) {
            Class annotationType = parameterAnnotation.annotationType();
            if (annotationType == PathVariable.class) {
                String name = PathVariable.class.cast(parameterAnnotation).value();
                nameParam(data, name, paramIndex);
                isHttpParam = true;
            }

            if (annotationType == RequestBody.class)
                handleProducesAnnotation(data, "application/json");

            if (annotationType == RequestParam.class) {
                String name = RequestParam.class.cast(parameterAnnotation).value();
                Collection query = addTemplatedParam(data.template().queries().get(name), name);
                data.template().query(name, query);
                nameParam(data, name, paramIndex);
                isHttpParam = true;
            }
        }
        return isHttpParam;
    }

    protected Collection addTemplatedParam(Collection possiblyNull, String name) {
        if (possiblyNull == null) {
            possiblyNull = new ArrayList();
        }
        possiblyNull.add(String.format("{%s}", name));
        return possiblyNull;
    }

}