前言

Feign的中文名稱翻譯過來是偽裝
那麼Feign偽裝的是什麼呢？答案很明確，Feign偽裝的是服務提供者。
Feign可以用來做什麼？既然能偽裝，當然能提供服務提供者的功能，即RPC呼叫服務提供者功能。

一、構建Feign

step1
新建一個SpringBoot專案，匯入web，feign，eureka client的pom依賴；這種依賴在各種IDE及SpringBoot構建網頁上都是直接輸入關鍵字按Enter就可以的

eureka:
  client:
    serviceUrl:
      defaultZone: http://server1:20001/eureka/
server:
  port: 8766
spring:
  application:
    name: service-feign
 

step3
配置負載均衡策略，新建一個類，配置bean Irule就可以了

import com.netflix.loadbalancer.IRule;
import com.netflix.loadbalancer.RandomRule;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class LoadBalancerConfig {
    @Bean
    public IRule getRule() {
        return new RandomRule();
    }
}
 

step4
主類開啟Feign註解@EnableFeignClients，即允許開啟Feign

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;
import org.springframework.cloud.openfeign.EnableFeignClients;
@EnableEurekaClient
@EnableFeignClients
@SpringBootApplication
public class FeignApplication {

    public static void main(String[] args) {
        SpringApplication.run(FeignApplication.class, args);
    }
}
 

step5
關鍵步驟來了，建立一個偽服務提供者介面（不需要實現），你偽裝誰@FeignClient的value就寫誰的名字。呼叫哪個介面就在RequestMapping 的value標註那個介面的url，方法名隨便起，引數要給人間傳過去

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;

@FeignClient(value = "service-hi")
public interface ServiceFeign {
    @RequestMapping(value = "/hi", method = RequestMethod.GET)
    String sayHi(@RequestParam(value = "name") String name);
}

step6
建立一個Controller便於前端觀察

@RestController
public class FeignController {
    
    @Autowired
    private ServiceFeign serviceFeign;

    @GetMapping(value = "/hi")
    public String sayHi(@RequestParam String name) {
        return serviceFeign.sayHi(name);
    }
}

step7
啟動eureka server，啟動三個service-hi，啟動service-feign，點選service-feign

總結