一.简介

SpringCloud是基于Restful的远程调用框架，引入Ribbon负载均衡组件后还需要客户端使用RestTemplate调用远程接口，操作起来还显得繁琐。SpringCloud提供了远程接口映射，将远程Restful服务映射为远程接口，消费端注入远程接口即可实现方法调用。

二.流程

1.新建远程接口映射模块service-api，并引入Feign接口映射依赖

 <dependencies>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-feign</artifactId>
    </dependency>
</dependencies>

2.编写接口映射接口

package com.vincent.service;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

@FeignClient("SERVICE-USER")
@RequestMapping("/service-user")
public interface IUserService {
    @GetMapping("/detail")
    Object detail(@RequestParam("id") Integer id);
}

3.配置消费端application.yml

server:
  port: 9001

eureka:
  client:
    service-url:
      defaultZone: http://localhost:7001/service-eureka/eureka
    register-with-eureka: false

4.消费端添加映射模块依赖

 <dependency>
    <groupId>com.vincent</groupId>
    <artifactId>service-api</artifactId>
    <version>1.0-SNAPSHOT</version>
</dependency>

5.客户端注入需要使用的服务接口映射

package com.vincent.controller;



import com.vincent.service.IUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;


@RestController
public class UserController {

    @Autowired
    private IUserService userService;

    @GetMapping("/detail")
    public Object detail(Integer id){
        return this.userService.detail(id);
    }
}

5.编写消费端启动类

package com.vincent;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.netflix.feign.EnableFeignClients;


@SpringBootApplication
@EnableFeignClients({"com.vincent.service"})
@EnableEurekaClient
public class ConsumerApp {
    public static void main(String[] args) {
        SpringApplication.run(ConsumerApp.class,args);
    }

}

@EnableFeignClients 定义Feign接口映射扫描包，IOC容器会自动创建接口实现类

6.访问 http://localhost:9001/detail?id=1

三.总结

Feign接口映射服务端Restful接口会自动依赖Ribbon组件，实现客户端负载均衡。使用接口调用消费端远程接口就像调用本地方法一样。