SpringCloudAlibaba-Sentinel-整合RestTemplate-Feign

Sentinel API

Github : WIKI

• Sphu（指明要保护的资源名称）
• Tracer（指明调用来源, 异常统计接口）
• ContextUtil（标示进入调用链入口）

• 流控规则 (针对来源属性)

  @GetMapping("/test-sentinel-api")
      public String testSentinelAPI(@RequestParam(required = false) String a) {
          String resourceName = "test-sentinel-api";
          
          ContextUtil.enter(resourceName, "user-center-service");
          // 定义一个 sentinel 保护的资源，名称是 test-sentinel-api
          Entry entry = null;
          try {entry = SphU.entry(resourceName);
              // ... 被保护的业务逻辑处理
              if (StringUtils.isEmpty(a)) {
                  // Sentinel 默认只会统计 BlockException & BlockException 的子类，如果想统计其他异常信息，添加 Tracer
                  throw new IllegalArgumentException("A is not empty.");
              }
              return a;
              // block Exception: 如果被保护的资源被限流或者降级了，就会抛异常出去
          } catch (BlockException e) {log.error("我被限流啦！！{}", e);
              return "我被限流啦！！";
          } catch (IllegalArgumentException argEx) {
              // 统计当前异常发生次数 / 占比
              Tracer.trace(argEx);
              return "非法参数信息";
          } finally {if (entry != null) {entry.exit();
              }
              ContextUtil.exit();}
      }

• 降级规则

  @GetMapping("/test-sentinel-api")
      public String testSentinelAPI(@RequestParam(required = false) String a) {
  
          // 定义一个 sentinel 保护的资源，名称是 test-sentinel-api
          Entry entry = null;
          try {entry = SphU.entry("test-sentinel-api");
              // ... 被保护的业务逻辑处理
              if (StringUtils.isEmpty(a)) {
                  // Sentinel 默认只会统计 BlockException & BlockException 的子类，如果想统计其他异常信息，添加 Tracer
                  throw new IllegalArgumentException("A is not empty.");
              }
              return a;
              // block Exception: 如果被保护的资源被限流或者降级了，就会抛异常出去
          } catch (BlockException e) {log.error("我被限流啦！！{}", e);
              return "我被限流啦！！";
          } catch (IllegalArgumentException argEx) {
              // 统计当前异常发生次数 / 占比
              Tracer.trace(argEx);
              return "非法参数信息";
          } finally {if (entry != null) {entry.exit();
              }
          }
  
      }

Sentinel Annotation

源码：com.alibaba.csp.sentinel.annotation.aspectj.SentinelResourceAspect & com.alibaba.csp.sentinel.annotation.aspectj.AbstractSentinelAspectSupport

• SentinelResource 使用该注解重构上述方法

      @GetMapping("/test-sentinel-resource")
      @SentinelResource(value = "test-sentinel-api", blockHandler = "blockException", fallback = "fallback")
      public String testSentinelResource(@RequestParam(required = false) String a) {
          // ... 被保护的业务逻辑处理
          if (StringUtils.isEmpty(a)) {
              // Sentinel 默认只会统计 BlockException & BlockException 的子类，如果想统计其他异常信息，添加 Tracer
              throw new IllegalArgumentException("A is not empty.");
          }
          return a;
      }
  
      /**

   */
  public String blockException(String a, BlockException e) {log.error("限流了,{}", e);
      return "blockHandler 对应《限流规则》";
  }

  /**
   * testSentinelResource fallback method
   * {@link SentinelResource} #fallback 在 < 1.6 的版本中，不能补货 BlockException
   */
  public String fallback(String a) {return "fallback 对应《降级规则》";}

#### RestTemplate 整合 Sentinel

使用 `@SentinelRestTemplate`.

`resttemplate.sentinel.enabled` 可以开关是否启用该注解。（开发阶段很有意义。）源码：`com.springframework.cloud.alibaba.sentinel.custom.SentinelBeanPostProcessor`

@Bean
@LoadBalanced
@SentinelRestTemplate
public RestTemplate restTemplate() {

return new RestTemplate();

}

@Autowired
private RestTemplate restTemplate;
…

#### Feign 整合 Sentinel

配置文件中添加 `feign.sentinel.enabled: true` 来开启

![image-20190718210655357](/Users/zhangpan/Library/Application Support/typora-user-images/image-20190718210655357.png)

1. 编写 fallback 类，实现 feign client

@Component
public class UserCenterFeignClientFallback implements IUserCenterFeignClient {

   @Override
   public UserDTO findById(Long userId) {UserDTO userDTO = new UserDTO();
       userDTO.setWxNickname("默认用户");
       return userDTO;
   }

}

@Slf4j
@Component
public class UserCenterFeignClientFallbackFactory implements FallbackFactory<IUserCenterFeignClient> {

   @Override
   public IUserCenterFeignClient create(Throwable cause) {return new IUserCenterFeignClient() {
           @Override
           public UserDTO findById(Long userId) {log.warn("远程调用被限流 / 降级，{}", cause);
               UserDTO userDTO = new UserDTO();
               userDTO.setWxNickname("默认用户");
               return userDTO;
           }
       };
   }

}

2. 应用 fallback class

/**

* IUserCenterFeignClient for 定义 user-center feign client
* fallbackFactory 可以拿到异常信息
* fallback 无法拿到异常信息
*
* @author <a href="mailto:magicianisaac@gmail.com">Isaac.Zhang | 若初 </a>
* @since 2019/7/15
*/

@FeignClient(name = “user-center”,

       // fallback = UserCenterFeignClientFallback.class,
       fallbackFactory = UserCenterFeignClientFallbackFactory.class

)
public interface IUserCenterFeignClient {

   @GetMapping(path = "/users/{userId}")
   public UserDTO findById(@PathVariable Long userId);

}

3. 启动应用，设置流控规则，结果展示如下

{

   id: 1,
   ...
   wxNickName: "默认用户"

}

源码：`org.springframework.cloud.alibaba.sentinel.feign.SentinelFeign`