使用Feign负载均衡

Feign 也是在客户端的负载均衡。其也集成了Ribbon负债均衡，它与Ribbon不同的是通过肺功能只要定义

服务绑定接口且以声明式的方法，优雅而简单的实现了服务的调用。

下面介绍使用步骤：

1.建立一个客户端消费者module。

pom文件内容：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>microservicecloud</artifactId>
        <groupId>com.atguigu.springcloud</groupId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>microservicecloud-consumer-dept-feign</artifactId>
    <dependencies>
        <dependency><!-- 自己定义的api -->
            <groupId>com.atguigu.springcloud</groupId>
            <artifactId>microservicecloud-api</artifactId>
            <version>${project.version}</version>
        </dependency>
        <!-- feign相关-->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-feign</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- Ribbon相关 Ribbon是基于客户端的负载均衡 -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-ribbon</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>
        <!-- 修改后立即生效，热部署 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>springloaded</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
        </dependency>
    </dependencies>

</project>

2.配置yaml：

server:
  port: 8000
feign:
  hystrix:
    enabled: true

eureka:
  client:
    register-with-eureka: false
    service-url:
      defaultZone: http://eureka7001.com:7001/eureka/,http://eureka7002.com:7002/eureka/,http://eureka7003.com:7003/eureka/

3.编写controller：

package com.atguigu.springcloud.controller;

import com.atguigu.springcloud.entities.Dept;
import com.atguigu.springcloud.service.DeptClientService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import java.util.List;

/**
 * 使用restTemplate访问restful接口非常的简单粗暴无脑。
 * (url, requestMap, ResponseBean.class)这三个参数分别代表
 * REST请求地址、请求参数、HTTP响应转换被转换成的对象类型。
 */
@RestController
public class DeptController_Consumer {
    @Autowired
    private DeptClientService service = null;//这个接口待会会在api工程里建立！

    @RequestMapping(value = "/consumer/dept/get/{id}")
    public Dept get(@PathVariable("id") Long id)
    {
        return this.service.get(id);
    }

    @RequestMapping(value = "/consumer/dept/list")
    public List<Dept> list()
    {
        return this.service.list();
    }

    @RequestMapping(value = "/consumer/dept/add")
    public Object add(Dept dept)
    {
        return this.service.add(dept);
    }
}

4.主启动类：

@SpringBootApplication(scanBasePackages ="com.atguigu.springcloud" )
@EnableEurekaClient
@EnableFeignClients(basePackages= {"com.atguigu.springcloud"})
public class DeptConsumer80_Feign_App {
    public static void main(String[] args) {
        SpringApplication.run(DeptConsumer80_Feign_App.class,args);

    }
}

5.修改api工程：

在pom文件中添加feign的依赖：

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

新建立DeptClientService接口，并且添加注解：

@FeignClient(value = "MICROSERVICECLOUD-DEPT")
public interface DeptClientService
{
  @RequestMapping(value = "/dept/get/{id}",method = RequestMethod.GET)
  public Dept get(@PathVariable("id") long id);
 
  @RequestMapping(value = "/dept/list",method = RequestMethod.GET)
  public List<Dept> list();
 
  @RequestMapping(value = "/dept/add",method = RequestMethod.POST)
  public boolean add(Dept dept);
}

这样就完事了，完整工程地址：https://hn.devcloud.huaweicloud.com/codehub/project/db863c4dd09b44e1949853aa22197df3/codehub/7172321/home

  Feign通过接口的方法调用Rest服务（之前是Ribbon+RestTemplate），
该请求发送给Eureka服务器（http://MICROSERVICECLOUD-DEPT/dept/list）,
通过Feign直接找到服务接口，由于在进行服务调用的时候融合了Ribbon技术，所以也支持负载均衡作用。