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 {

    @Autowired
    private 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 {
    @Override
    public 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;



    @Bean
    public 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

    @Bean
    public 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