SpringCloud：Feign（工程构建、负载均衡）

1、概念

（1）概述

Feign是一个声明式的Web服务客户端，使得编写Web服务客户端变得非常容易，只需要创建一个接口，然后在上面添加注解即可，能够实现客户端的负载均衡。

2、Feign工程构建

（1）模仿消费者（80）新建一个Feign模块，并添加Feign的依赖

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

（2）修改公共模块

• 添加Feign的依赖

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

• 创建接口

注解的参数中带有微服务的名称，通过该名称获取服务

@FeignClient(value = "PROVIDER")
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);
}

（3）创建消费者模块

@RestController
public class DeptConsumerController {
    @Autowired
    private DeptClientService service = null;

    @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);
    }
}

• 启动类

@SpringBootApplication(exclude= {DataSourceAutoConfiguration.class,HibernateJpaAutoConfiguration.class})
@EnableEurekaClient
@EnableFeignClients(basePackages= {"com.zhb"})
@ComponentScan("com.zhb")
public class DeptConsumer80_Feign_App {
    public static void main(String[] args) {
        SpringApplication.run(DeptConsumer80_Feign_App.class,args);
    }
}

 （4）RestTemplate 方式

消费者模块代码：

与Feign相比，RestTemplate 方式不需要在公共类里面添加接口，Feign是在接口里面的注解添加微服务的名称即可。

@RestController
public class DeptConsumerController {
    private static final String REST_URL_PREFIX = "http://PROVIDER";

    @Autowired
    private RestTemplate restTemplate;

    @RequestMapping(value = "/consumer/dept/add")
    public boolean add(Dept dept) {
        return restTemplate.postForObject(REST_URL_PREFIX + "/dept/add", dept, Boolean.class);
    }

    @RequestMapping(value = "/consumer/dept/get/{id}")
    public Dept get(@PathVariable("id") Long id) {
        return restTemplate.getForObject(REST_URL_PREFIX + "/dept/get/" + id, Dept.class);
    }

    @SuppressWarnings("unchecked")
    @RequestMapping(value = "/consumer/dept/list")
    public List<Dept> list() {
        return restTemplate.getForObject(REST_URL_PREFIX + "/dept/list", List.class);
    }

}

配置类：

   @Bean
    @LoadBalanced
    public RestTemplate template(){
        return  new RestTemplate();
    }

 （5）负载均衡

Feign集成了Ribbon，并通过轮询的方式实现了客户端的负载均衡