一、什么是Feign

1. Feign是一个http请求调用的轻量级框架，可以以Java接口注解的方式调用Http请求，而不用像Java中通过封装HTTP请求报文的方式直接调用。Feign通过处理注解，将请求模板化，当实际调用的时候，传入参数，根据参数再应用到请求上，进而转化成真正的请求，这种请求相对而言比较直观。
2. Feign被广泛应用在Spring Cloud 的解决方案中，是学习基于Spring Cloud 微服务架构不可或缺的重要组件。
3. Feign具有可插拔的注解特性，可使用Feign注解和JAX-RS注解。
4. Feign默认集成了Ribbon，并和Eureka结合，默认实现了负载均衡的效果。

二、下面来看看具体实现

首先创建Feign模块，cloud-demo-feign

下面是项目结构

pom文件如下

<?xml version="1.0"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><modelVersion>4.0.0</modelVersion><parent><groupId>com.hewl</groupId><artifactId>cloud-demo-parent</artifactId><version>0.0.1-SNAPSHOT</version></parent><artifactId>cloud-demo-feign</artifactId><name>cloud-demo-feign</name><url>http://maven.apache.org</url><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-netflix-eureka-client</artifactId></dependency><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId></dependency></dependencies>
</project>
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application.yml文件如下

server:port: 8811 # 你的端口
spring:application:name: feign
eureka:client:service-url:defaultZone: http://admin:admin@server1:8761/eureka/,http://admin:admin@server2:8762/eureka/
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启动类内容如下，加上@EnableFeignClients注解开启Feign的功能

package com.hewl;import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;@SpringBootApplication
@EnableEurekaClient
@EnableFeignClients
public class FeignApplication {public static void main(String[] args) {SpringApplication.run(FeignApplication.class, args);}
}
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定义Feign接口，SchedualCilentName

package com.hewl.feign;import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;@FeignClient(value="service-eureka-client")
public interface SchedualCilentName {@GetMapping(value = "/test")public String testFromClientOne(@RequestParam("name") String name);}
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定义对外的controller

package com.hewl.controller;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;import com.hewl.feign.SchedualCilentName;@RestController
public class TestController {@Autowiredpublic SchedualCilentName schedualCilentName;@GetMapping(value="/test")public String test (String name) {return schedualCilentName.testFromClientOne(name);}
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按顺序启动项目

1. 启动eureka-server
2. 修改端口分别启动两次eureka-client
3. 启动feign客户端

访问localhost:8811/test?name=张三，访问成功并且已经成功启动负载均衡