Spring cloud实战-Fegin简易使用

Fegin、Eureka

Fegin在spring cloud中，比较常见的是用来类型RPC一样的远程过程调用。

项目地址：

AG-Admin：http://git.oschina.net/geek_qi/ace-security

简易使用

Maven依赖

    org.springframework.cloud
    spring-cloud-starter-feign


    org.springframework.cloud
    spring-cloud-starter-eureka

application.yml 配置

#注册eureka服务
eureka:
    instance:
        statusPageUrlPath: ${management.context-path}/info
        healthCheckUrlPath: ${management.context-path}/health
    client:
        serviceUrl:
            defaultZone: http://localhost:8761/eureka/
#请求和响应GZIP压缩支持
feign:
  compression:
    request:
      enabled: true
      mime-types: text/xml,application/xml,application/json
      min-request-size: 2048
    response:
      enabled: true

基于Eureka的Fegin写法

// “back”为Euerka中服务注册名
@FeignClient("back")
public interface IUserService {
  @RequestMapping(value = "/service/user/username/{username}", method = RequestMethod.GET)
  public UserInfo getUserByUsername(@PathVariable("username") String username);
  @RequestMapping(value = "/service/user/{id}/permissions", method = RequestMethod.GET)
  public List getPermissionByUserId(@PathVariable("id") String userId);
}

Fegin Bean的调用

@Controller
@RequestMapping("")
public class UserPermissionController {
    @Autowired
    private IUserService userService;
    @RequestMapping(value = "/user/system",method = RequestMethod.GET)
    @ResponseBody
    public String getUserSystem(){
       return userService.getSystemsByUsername("admin");
    }
}

Feign与Hystrix

如果Hystrix在classpath中，Feign会默认将所有方法都封装到断路器中。Returning a com.netflix.hystrix.HystrixCommand is also available。这样一来你就可以使用Reactive Pattern了。(调用.toObservalbe()或.observe()方法，或者通过.queue()进行异步调用)。

将feign.hystrix.enabled=false参数设为false可以关闭对Hystrix的支持。

如果想只关闭指定客户端的Hystrix支持，创建一个Feign.Builder组件并标注为@Scope(prototype)：

@Configuration
public class FooConfiguration {
    @Bean
    @Scope("prototype")
    public Feign.Builder feignBuilder() {
        return Feign.builder();
    }
}

Feign对Hystrix Fallback的支持

Hystrix支持fallback的概念，即当断路器打开或发生错误时执行指定的失败逻辑。要为指定的@FeignClient启用Fallback支持， 需要在fallback属性中指定实现类：

@FeignClient(name = "hello", fallback = HystrixClientFallback.class)
protected interface HystrixClient {
    @RequestMapping(method = RequestMethod.GET, value = "/hello")
    Hello iFailSometimes();
}

static class HystrixClientFallback implements HystrixClient {
    @Override
    public Hello iFailSometimes() {
        return new Hello("fallback");
    }
}

Fegin的继承

Feign可以通过Java的接口支持继承。你可以把一些公共的操作放到父接口中，然后定义子接口继承之：

接口

public interface UserService {

    @RequestMapping(method = RequestMethod.GET, value ="/users/{id}")
    User getUser(@PathVariable("id") long id);
}

实现

@RestController
public class UserResource implements UserService {

}

客户端

@FeignClient("users")
public interface UserClient extends UserService {

}