在日常的开发中，当遇到一个请求需要传递多个参数时，我们习惯将参数封装到一个POJO对象中，已提高程序的可读性和简化编写。但是在使用SpringCloud时，Feign对SpringMVC注解支持并不完善，其中一点就是，当发送的GET请求携带多个参数时，不能使用POJO来封装参数，这个就比较蛋疼了。一种使之支持GET请求POJO传递参数的方法如下:

添加Maven依赖

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <dependency>
            <groupId>com.netflix.feign</groupId>
            <artifactId>feign-httpclient</artifactId>
            <version>8.15.1</version>
        </dependency>
   
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-hystrix</artifactId>
            <version>10.2.0</version>
            <scope>compile</scope>
        </dependency>

        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
        </dependency>
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-okhttp</artifactId>
        </dependency>

application.yml

        feign:
          hystrix:
            enabled: true
          httpclient:
            enabled: true
          okhttp:
            enabled: true

添加对GET请求的拦截器

        
import com.alibaba.fastjson.JSON;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import feign.RequestInterceptor;
import feign.RequestTemplate;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpMethod;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;

import javax.annotation.Resource;
import java.io.IOException;
import java.util.*;

/**
 * 拦截Fegin的get请求，使之支持get请求pojo传参
 */
@Component
public class FeignRequestInterceptor implements RequestInterceptor {
    private static final Logger log = LoggerFactory.getLogger(FeignRequestInterceptor.class);
    @Resource
    private ObjectMapper objectMapper;

    @Override
    public void apply(RequestTemplate template) {
        if (HttpMethod.GET.name().equals(template.method())
                && null != template.body()) {
            try {
                JsonNode jsonNode = objectMapper.readTree(template.body());
                template.body(null);

                Map<String, Collection<String>> queries = new HashMap<>();
                buildQuery(jsonNode, "", queries);
                template.queries(queries);
            } catch (IOException e) {
                log.error("【拦截GET请求POJO方式】-出错了：{}", JSON.toJSONString(e));
                throw new RuntimeException();
            }
        }
    }

    private void buildQuery(JsonNode jsonNode, String path, Map<String, Collection<String>> queries) {
        // 叶子节点
        if (!jsonNode.isContainerNode()) {
            if (jsonNode.isNull()) {
                return;
            }
            Collection<String> values = queries.get(path);
            if (null == values) {
                values = new ArrayList<>();
                queries.put(path, values);
            }
            values.add(jsonNode.asText());
            return;
        }
        // 数组节点
        if (jsonNode.isArray()) {
            Iterator<JsonNode> it = jsonNode.elements();
            while (it.hasNext()) {
                buildQuery(it.next(), path, queries);
            }
        } else {
            Iterator<Map.Entry<String, JsonNode>> it = jsonNode.fields();
            while (it.hasNext()) {
                Map.Entry<String, JsonNode> entry = it.next();
                if (StringUtils.hasText(path)) {
                    buildQuery(entry.getValue(), path + "." + entry.getKey(), queries);
                } else {  // 根节点
                    buildQuery(entry.getValue(), entry.getKey(), queries);
                }
            }
        }
    }

}

其他

此时你的应用程序就可以通过POJO封装参数向其他服务发起调用了。但是如果你请求的Content-Type是application/json的，那么你要需要指定请求的consumes为consumes = MediaType.APPLICATION_JSON_VALUE。