spring cloud2.0学习笔记之Feign实战

背景

• springCloud:Finchley.RELEASE

简介

Feign是SpringCloud体系中声明式Rest客户端，通过简单配置、创建接口和注解即可实现Restful服务的调用。而且开始支持SpringMvc了。

简单应用

• 依赖：org.springframework.cloud:spring-cloud-starter-openfeign

• 入口加@EnableFeignClients注解

• 创建相应接口、加注解 

//入口类
@SpringBootApplication
@EnableFeignClientspublic class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}
//原型接口声明
@FeignClient("stores")public interface StoreClient {
    @RequestMapping(method = RequestMethod.GET, value = "/stores")
    List<Store> getStores();    
    @RequestMapping(method = RequestMethod.POST, value = "/stores/{storeId}", consumes = "application/json")
    Store update(@PathVariable("storeId") Long storeId, Store store);
}

开启Feign断路器和上下文支持

• feign.hystrix.enabled=true

# To disable Hystrix in Feignfeign:
  hystrix:
    enabled: true# To set thread isolation to SEMAPHORE# 将断路器隔离级别由默认的线程隔离调整为信号灯hystrix:
  command:    default:
      execution:
        isolation:
          strategy: SEMAPHORE

断路器回调

断路器支持回退，就是当断路器开启或接口出现错误时执行回调定义的方法，返回预先定义好的结果。 开启回调支持只需在@FeignClient注解中配置fallback参数为接口的回调实现类，并且回调实现类要被注解为Spring Bean(可以通过@Component，@Service等注解实现，详情见Spring4的注解文档)。

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

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

如果需要知道回退原因可以通过回退工厂来实现，代码实例如下：

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

@Componentstatic class HystrixClientFallbackFactory implements FallbackFactory<HystrixClient> {
    @Override    public HystrixClient create(Throwable cause) {        
        return new HystrixClient() {
            @Override            
            public Hello iFailSometimes() {                
                return new Hello("fallback; reason was: " + cause.getMessage());
            }
        };
    }
}

Feign支持继承接口

Feign支持接口继承的方式，将操作通过接口来形成契约。

//生产者的控制层接口public interface UserService {

    @RequestMapping(method = RequestMethod.GET, value ="/users/{id}")
    User getUser(@PathVariable("id") long id);
}
//生产者的控制器实现
@RestController
public class UserResource implements UserService {}
//消费端的Feign接口定义
package project.user;
@FeignClient("users")
public interface UserClient extends UserService {}

压缩支持

开启压缩可以有效节约网络资源，但是会增加CPU压力，建议把最小压缩的文档大小适度调大一点

//开启压缩
feign.compression.request.enabled=true
feign.compression.response.enabled=true

//配置压缩文档类型及最小压缩的文档大小
feign.compression.request.mime-types=text/xml,application/xml,application/json
feign.compression.request.min-request-size=2048

日志配置

• 消费服务的接口所在包，必须是debug

# 日志支持logging.level.project.user.UserClient: DEBUG

• 定义自定义配置类,定义日志级别

@Configurationpublic class FooConfiguration {
    @Bean
    Logger.Level feignLoggerLevel() {        
        return Logger.Level.FULL;
    }
}

• 日志级别
  

• NONE, No logging (DEFAULT).

• BASIC, Log only the request method and URL and the response status code and execution time.

• HEADERS, Log the basic information along with request and response headers.

• FULL, Log the headers, body, and metadata for both requests and responses.

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