spring cloud2.0學習筆記之Feign實戰

背景

• springCloud:Finchley.RELEASE

簡介

Feign是SpringCloud體系中聲明式Rest客戶端，透過簡單配置、建立介面和註解即可實現Restful服務的呼叫。而且開始支持SpringMvc了。

簡單應用程式

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

• 入口加@ EnableFeignClients註解

• 建立對應介面、加註解 

//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);
}

開啟Feign斷路器與上下文支援

#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

斷路器回呼

• 斷路器支援回退，就是當斷路器開啟或介面出現錯誤時執行回呼定義的方法，傳回預先定義好的結果。開啟回呼支援只需在@FeignClient註解中配置fallback參數為介面的回呼實現類，並且回呼實現類別要被註解為Spring Bean(可以透過@Component，@Service等註解實現，詳情請參閱Spring4的註解文件)。

  @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透過回退工廠來實現，程式碼實例如下：

@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支援繼承介面

• Feign支援介面繼承的方式，將操作透過介面來形成契約。

  //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 {}

  壓縮支援

開啟壓縮可以有效節約網路資源，但是會增加CPU壓力，建議將最小壓縮的文件大小適度調大一點

//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

• 日誌配置

  
  

消費服務的介面所在包，必須是debug

• #

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

• 定義自訂組態類別,定義日誌等級

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

• 日誌等級

#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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