在使用spring boot调用第三方api中，常用的是okhttp、apache http client等，但是直接使用下来还是有点繁琐，需要手动转换实体。
在springcloud中有个openfeign调用，第一次体验到调用接口还能这么丝滑。注解写道接口上，配置一下，其他交给框架处理。搜了一下这种方式叫做声明式调用。类似的还有Retrofit、forest框架。
openfeign集成到springboot中有何优点：openfeign吸收了Retrofit框架的优点，做了声明式API，但是没有Retrofit多余的Call层。forest是一款国产优秀的框架，单独使用问题不大，但对于后续升级到cloud的boot项目，共存时存在不少问题，并且对上传大文件部分场景的支持有点问题。
这里分两步，先介绍@RequestLine注解调用，后介绍@GetMapping的spring注解调用。
一、传统注解@RequestLine调用
1.加依赖
<!-- feign --><dependency><groupId>io.github.openfeign</groupId><artifactId>feign-core</artifactId><version>11.0</version></dependency><dependency><groupId>com.netflix.feign</groupId><artifactId>feign-jackson</artifactId><version>8.18.0</version></dependency>
2.写代码
以天气api接口为例
controller层
package com.vvvtimes.demo.controller;import com.vvvtimes.demo.common.dto.RestResponse;
import com.vvvtimes.demo.domain.dto.WeatherCityDTO;
import com.vvvtimes.demo.domain.mybatis.City;
import com.vvvtimes.demo.domain.vo.WeatherVo;
import com.vvvtimes.demo.service.WeatherService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;import java.util.List;@RestController
@RequestMapping("/weather")
public class WeatherController {@Autowiredprivate WeatherService weatherService;@RequestMapping(value = "city/{id:1[0-9]{8}}", method = {RequestMethod.POST, RequestMethod.GET})public RestResponse<WeatherVo> loadApi(@PathVariable("id") String id) {return weatherService.loadApi(id);}}service层
/*** 获取数据* @param id* @return*/@Cacheable(cacheNames = "weather_cache", key = "#id")// 从缓存获取，key为ID，缓存具体看 ehcache.xml 配置文件public RestResponse<WeatherVo> loadApi(String id) {RestResponse<WeatherVo> result =new RestResponse<>();WeatherVo weatherVo = sojsonApiClient.getCityWeather(id);if(weatherVo!=null && weatherVo.isSuccess()){result.setResult(weatherVo);}return result;}//client层
package com.vvvtimes.demo.client;import com.vvvtimes.demo.domain.vo.WeatherVo;
import feign.Param;
import feign.RequestLine;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;import java.util.Map;@Component
public interface SojsonApiClient {//@GetMapping(value = "/api/weather/city/{id}")@RequestLine("GET /api/weather/city/{id}")WeatherVo getCityWeather(@Param("id") String id);}
client拦截器
package com.vvvtimes.demo.client.interception;import feign.RequestInterceptor;
import feign.RequestTemplate;public class SojsonInterceptor implements RequestInterceptor {@Overridepublic void apply(RequestTemplate requestTemplate) {}
}
feign配置
package com.vvvtimes.demo.config;import com.vvvtimes.demo.client.IpinfoApiClient;
import com.vvvtimes.demo.client.SojsonApiClient;
import com.vvvtimes.demo.client.interception.IpinfoInterceptor;
import com.vvvtimes.demo.client.interception.SojsonInterceptor;
import feign.Feign;
import feign.jackson.JacksonDecoder;
import feign.jackson.JacksonEncoder;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;@Configuration
public class ApiRegisterConfig {@Value("${sojson.base.url:http://t.weather.sojson.com/}")private String sojsonRegisterUrl;@Beanpublic SojsonApiClient sojsonApiRegister() {return Feign.builder().encoder(new JacksonEncoder()).decoder(new JacksonDecoder()).requestInterceptor(new SojsonInterceptor()).target(SojsonApiClient.class, sojsonRegisterUrl);}}
3.测试访问
http://localhost:9000/weather/city/101010100
二、spring注解@GetMapping使用
上面使用的注解多少有点别扭，实际上我们可以通过feign-contract Feign的契约方式来使用spring的注解。
这里只对比上的代码讲解改造过程，不给出全代码
1.改造依赖
上面的feign依赖替换如下
<!-- feign --><dependency><groupId>io.github.openfeign</groupId><artifactId>feign-core</artifactId><version>11.6</version></dependency><dependency><groupId>io.github.openfeign</groupId><artifactId>feign-spring4</artifactId><version>11.6</version></dependency><dependency><groupId>io.github.openfeign</groupId><artifactId>feign-jackson</artifactId><version>11.6</version></dependency><dependency><groupId>io.github.openfeign</groupId><artifactId>feign-httpclient</artifactId><version>11.6</version></dependency><dependency><groupId>io.github.openfeign.form</groupId><artifactId>feign-form</artifactId><version>3.8.0</version></dependency>2.配置契约
ApiRegisterConfig的Bean加一句.contract(new SpringContract())
对应bean代码如下
@Beanpublic SojsonApiClient sojsonApiRegister() {return Feign.builder().encoder(new JacksonEncoder()).decoder(new JacksonDecoder()).requestInterceptor(new SojsonInterceptor()).contract(new SpringContract()).target(SojsonApiClient.class, sojsonRegisterUrl);}3.改注解
将@RequestLine注解改成@GetMapping注解，代码如下
@GetMapping(value = "/api/weather/city/{id}")//@RequestLine("GET /api/weather/city/{id}")WeatherVo getCityWeather(@PathVariable("id") String id);至此改造完成。
注意：本文没有设置feign的全局拦截器，因为在第三方接口中，每种接口的鉴权方式不一样，建议每种类型的接口单独设置拦截器做鉴权
