Spring Cloud提供了Ribbon和Feign作为客户端的负载均衡。

前面使用了Ribbon做客户端负载均衡，使用Hystrix做容错保护，这两者被作为基础工具类框架被广泛地应用在各个微服务的实现中。SpringCloudFeign是将两者做了更高层次的封装以简化开发。它基于Netflix Feign实现，整合了SpringCloud Ribbon和SpringCloud Hystrix，除了提供这两者的强大功能外，还提供了一种声明是的Web服务客户端定义的方式。SpringCloud Feign在NetFixFeign的基础上扩展了对SpringMVC注解的支持，在其实现下，我们只需创建一个接口并用注解的方式来配置它，即可完成对服务提供方的接口绑定。简化了SpringCloud Ribbon自行封装服务调用客户端的开发量。

在Spring Cloud下，使用Ribbon直接注入一个RestTemplate对象即可，此RestTemplate已做好负载均衡的配置；而使用Feign只需定义个注解，有@FeignClient注解的接口，然后使用@RequestMapping注解在方法上映射远程的REST服务，此方法也是做好了负载均衡配置。

新建项目 feign-consumer https://start.spring.io/
更新配置 application.properties

spring.application.name=compute-consume-feign
server.port=2231
eureka.client.serviceUrl.defaultZone=http://localhost:1111/eureka/

启动类加注解 @EnableFeignClients

package com.baoguoding.feignconsumer;

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


@SpringBootApplication
@EnableFeignClients
@EnableDiscoveryClient
public class FeignConsumerApplication {

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

}

添加接口 HelloService

package com.baoguoding.feignconsumer.remote;

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("compute-service")
public interface HelloService {
    @RequestMapping(value="/add", method = RequestMethod.GET)
    String hello(@RequestParam("a") Integer a, @RequestParam("b") Integer b, @RequestParam("sn") Integer sn);
}

添加服务类 AddConsumerController

package com.baoguoding.feignconsumer.service;

import com.baoguoding.feignconsumer.remote.HelloService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

import java.util.concurrent.atomic.AtomicInteger;

@RestController
public class AddConsumerController {
    @Autowired
    HelloService helloService;

    private AtomicInteger sn = new AtomicInteger(0);

    @RequestMapping(value="/feign-consumer", method = RequestMethod.GET)
    public String helloConsumer(@RequestParam Integer a, @RequestParam Integer b) {
        return helloService.hello(a, b, sn.incrementAndGet());
    }
}

访问 http://127.0.0.1:2231/feign-consumer?a=1&b=3
熔断处理，服务降级，新增类 HelloServiceFallback

package com.baoguoding.feignconsumer.remote;

import org.springframework.stereotype.Service;

@Service
public class HelloServiceFallback implements HelloService {

    @Override
    public String hello(Integer a, Integer b, Integer sn) {
        System.out.println("HelloServiceFallback");
        return "fallback";
    }

}

更新 HelloService

package com.baoguoding.feignconsumer.remote;

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("compute-service")
@FeignClient(name="compute-service", fallback=HelloServiceFallback.class)
public interface HelloService {
    @RequestMapping(value="/add", method = RequestMethod.GET)
    String hello(@RequestParam("a") Integer a, @RequestParam("b") Integer b, @RequestParam("sn") Integer sn);
}

打开compute 下面的随机函数

更新配置 application.properties

feign.hystrix.enabled=true

访问 http://127.0.0.1:2231/feign-consumer?a=1&b=3

微服务：Feign

参考