一、代码示例

说明：此处使用的SpringBoot版本为2.1.13.RELEASE，SpringCloud版本为Greenwich.SR5
Feign可以理解为声明式调用REST方式。
此处就不再贴server与client的代码
1、maven依赖

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
    </dependencies>

2、application.yml

server:
  port: 9003
spring:
  application:
    name: feign
eureka:
  instance:
    hostname: localhost
    prefer-ip-address: true
    instance-id: feign-9003
  client:
    service-url:
      defaultZone: http://eureka7001:7001/eureka/,http://eureka7002:7002/eureka/,http://eureka7003:7003/eureka/
#info信息
info:
  app:
    name: feign-9003
  company:
    name: www.xxx.com
  build:
    artifactId: ${project.artifactId}
    version: ${project.version}

3、启动类
启动类增加注解@EnableFeignClients启动Feign

package org.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.openfeign.EnableFeignClients;

@SpringBootApplication
@EnableFeignClients
public class Feign9003Application {
    public static void main(String[] args) {
        SpringApplication.run(Feign9003Application.class,args);
    }
}

4、其他java类
Feign对应的接口类
定义一个接口，增加@FeignClient(value = "CLIENT")，@FeignClient对应的VALUE为需要调用的服务名，接口中的方法与需要调用服务的方法一致并增加@GetMapping("/hello/{name}")(根据调用的方式选择)
@FeignClient会将接口注入到容器

package org.example.service;

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

@FeignClient(value = "CLIENT")
public interface FeignService {

    @GetMapping("/hello/{name}")
    public String hello(@PathVariable(value = "name") String name);
}

Controller类
注入前面定义的Feign接口类

package org.example.controller;

import org.example.service.FeignService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @Autowired
    private FeignService feignService;

    @GetMapping("/hello/{name}")
    public String hello(@PathVariable String name){
        return feignService.hello(name);
    }
}

2、测试验证

先后启动server、client、feign对应的服务，访问http://localhost:7001/

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