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Spring Cloud （5） —— Feign 调用 provider 和负载均衡

关于 Feign

Feign是一个声明式的伪Http客户端，它使得 Http 客户端编码变得更简单。使用Feign，只需要创建一个接口并注解。它具有可插拔的注解特性，可使用Feign 注解和 JAX-RS 注解。Feign 支持可插拔的编码器和解码器。Feign 默认集成了 Ribbon，自然就实现了负载均衡的效果。

Feign 的使用

新建模块 spring-cloud.s04.store-feign

在 pom 中添加依赖

<dependencies>
    <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-starter-openfeign</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-actuator</artifactId>
    </dependency>
  </dependencies>

添加配置文件

application.yml

server:
  port: 31002
spring:
  application:
    name: store-feign
eureka:
  client:
    serviceUrl:
      defaultZone: http://user:123123@localhost:34001/eureka/
  instance:
    instance-id: ${spring.cloud.client.ip-address}:${server.port}/${spring.application.name}
    prefer-ip-address: true
    lease-renewal-interval-in-seconds: 10
    lease-expiration-duration-in-seconds: 30

创建启动类 ..StoreFeign

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

为了专注 Feign 的使用，将 Feign 的应用提取到 service 层，与 controller 层的注解分开。创建 接口 ..StoreFeignService

/*
@FeignClient("") 参数填 Spring Cloud Provider 的应用名 ${spring.application.name}
 */
@FeignClient("album-provider")
public interface StoreFeignService {
  /*
  @RequestMapping() 默认参数是请求资源的地址，
  也可以指定请求的 Http Method @RequestMapping(value="/movie/movies",method=RequestMethod.GET)

  getMovies() 也可以算入参数，例如 getMovies(@RequestParam("name") String name) ，调用时比如传入的参数
   */
  @RequestMapping("/album/server-port")
  public String getProviderPort();
}

创建访问入口 ..StoreFeignController

@RestController
@RequestMapping("/store-feign")
public class StoreFeignController {

  @Autowired
  StoreFeignService storeFeignService;

  @RequestMapping("/album-provider-port")
  public String getProviderPort() {
    return storeFeignService.getProviderPort();
  }
}