2.3 服务消费者 - 2.3.2. Feign

Feign介绍

Feign是一个声明式的web service客户端，它使得编写web service客户端更为容易。创建接口，为接口添加注解，即可使用Feign。Feign可以使用Feign注解或者JAX-RS注解，还支持热插拔的编码器和解码器。Spring Cloud为Feign添加了Spring MVC的注解支持，并整合了Ribbon和Eureka来为使用Feign时提供负载均衡。

译自：http://projects.spring.io/spring-cloud/docs/1.0.3/spring-cloud.html

Feign示例

创建一个Maven项目，并在pom.xml添加如下内容：

<?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">
  <modelVersion>4.0.0</modelVersion>
  <artifactId>microservice-consumer-movie-feign</artifactId>
  <packaging>jar</packaging>
  <parent>
    <groupId>com.itmuch.cloud</groupId>
    <artifactId>spring-cloud-microservice-study</artifactId>
    <version>0.0.1-SNAPSHOT</version>
  </parent>
  <dependencies>
    <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-starter-eureka</artifactId>
    </dependency>
    <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-starter-feign</artifactId>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-actuator</artifactId>
    </dependency>
  </dependencies>
</project>

启动类：MovieFeignApplication.java

/**
 * 使用@EnableFeignClients开启Feign
 * @author eacdy
 */
@SpringBootApplication
@EnableFeignClients
@EnableDiscoveryClient
public class MovieFeignApplication {
  public static void main(String[] args) {
    SpringApplication.run(MovieFeignApplication.class, args);
  }
}

实体类：User.java

public class User {
  private Long id;
  private String username;
  private Integer age;
  ...
  // getters and setters
}

Feign测试类：UserFeignClient.java。

/**
 * 使用@FeignClient("microservice-provider-user")注解绑定microservice-provider-user服务，还可以使用url参数指定一个URL。
 * @author eacdy
 */
@FeignClient(name = "microservice-provider-user")
public interface UserFeignClient {
  @RequestMapping("/{id}")
  public User findByIdFeign(@RequestParam("id") Long id);
}

Feign的测试类：FeignController.java

@RestController
public class FeignController {
  @Autowired
  private UserFeignClient userFeignClient;
  @GetMapping("feign/{id}")
  public User findByIdFeign(@PathVariable Long id) {
    User user = this.userFeignClient.findByIdFeign(id);
    return user;
  }
}

application.yml

server:
  port: 8020
spring:
  application:
    name: microservice-consumer-movie-feign
eureka:
  client:
    serviceUrl:
      defaultZone: http://discovery:8761/eureka/
  instance:
    preferIpAddress: true
ribbon:
  eureka:
    enabled: true         # 默认为true。如果设置为false，Ribbon将不会从Eureka中获得服务列表，而是使用静态配置的服务列表。静态服务列表可使用：<client>.ribbon.listOfServers来指定。参考：http://projects.spring.io/spring-cloud/docs/1.0.3/spring-cloud.html#spring-cloud-ribbon-without-eureka
### 参考：https://spring.io/guides/gs/client-side-load-balancing/

同样的，启动该应用，多次访问http://localhost:8020/feign/1，我们会发现和Ribbon示例一样实现了负载均衡。

代码地址（任选其一）：

Feign代码地址：

http://git.oschina.net/itmuch/spring-cloud-study/tree/master/microservice-consumer-movie-feign
https://github.com/eacdy/spring-cloud-study/tree/master/microservice-consumer-movie-feign