捕获 Hystrix 回退引发的异常？

Question

我正在设计一个服务外观，并且我有一个如下所示的方法签名：

public Policy getPolicy(long policyId) throws PolicyNotFoundException

如果没有发生任何错误，则返回一个 Policy 对象（简单 POJO）。如果未找到请求的策略，则抛出已检查的异常 PolicyNotFoundException（仅作为参考 - 当涉及应用程序中异常处理的最佳实践时，我们遵循 this article）。

服务外观层之上的层（在本例中为Spring MVC RestController）知道如何处理此类 PolicyNotFoundException 并返回适当的负载。

我正在尝试通过执行以下操作将其合并到 HystrixCommand 中：

@HystrixCommand(groupKey = "PolicyService", fallbackMethod = "getPolicySafe", ignoreExceptions = { PolicyNotFoundException.class })
public Policy getPolicy(long policyId) throws PolicyNotFoundException {
    LOGGER.info("Getting policy {}", policyId);

    // Simulate some error condition for testing purposes
    throw new RuntimeException("Something happened!");
}

private Policy getPolicySafe(long policyId, Throwable t) throws PolicyNotFoundException {
    LOGGER.warn("Falling back to circuit-breaker for getting policy {}", policyId, t);
    throw new PolicyNotFoundException(policyId);
}

基本上，我希望我的断路器的行为就像原始查找未找到该策略一样。我遇到的问题是我从后备方法抛出的异常在某处的翻译中丢失了。我最终在上层看到的异常是命令方法抛出的 RuntimeException，而不是回退方法抛出的异常。有没有解决的办法？我也不想更改原始方法的合同，也不想让上面的层知道除了在找不到策略的情况下必须捕获 PolicyNotFoundException 之外的任何内容。此处需要的任何内容都应在此服务外观层中捕获。

我们将不胜感激任何和所有的帮助。谢谢！

Answer 1

所以根据@spencergibb 给出的链接——我可能在升级到 Hystrix 1.5.7 后找到了解决方案。此代码按预期工作

PolicyRestController.java

@RestController
@RequestMapping("/policies")
public class PoliciesApi {
  private static final Logger LOGGER = LoggerFactory.getLogger(PoliciesApi.class);

  @Autowired
  private PolicyService policyService;

  @RequestMapping(value = "/{policyId}", method = RequestMethod.GET, produces = { MediaTypes.POLICY_JSON_VALUE, MediaTypes.POLICY_XML_VALUE })
  public Policy getPolicy(@PathVariable long policyId) {
    try {
      // This just shown for simplicity. There is more to this method (input validation/etc)
      return this.policyService.getPolicy(policyId);
    }
    catch (PolicyNotFoundException ex) {
      // NotFoundException is a RuntimeException annotated with @ResponseStatus(HttpStatus.NOT_FOUND)
      // So the service returns a 404 to the client
      LOGGER.info("Policy {} wasn't found", ex.getPolicyId(), ex);
      throw new NotFoundException(String.format("Policy %s was not found", ex.getPolicyId()));
    }
  }
}

PolicyService.java

public interface PolicyService {
    @Cacheable("allPolicies")
    public List<Policy> getPolicies();

    @Cacheable("policies")
    public Policy getPolicy(long policyId) throws PolicyNotFoundException;
}

PolicyServiceImpl.java：

@Service
public class PolicyServiceImpl implements PolicyService {
  @HystrixCommand(groupKey = "PolicyService", fallbackMethod = "getPolicySafe", ignoreExceptions = { PolicyNotFoundException.class })
  public Policy getPolicy(long policyId) throws PolicyNotFoundException {
    LOGGER.info("Getting policy {}", policyId);

    // Simulate some error condition for testing purposes
    throw new RuntimeException("Something happened!");
  }

  @HystrixCommand(groupKey = "PolicyService", ignoreExceptions = { PolicyNotFoundException.class }, raiseHystrixExceptions = { HystrixException.RUNTIME_EXCEPTION })
  private Policy getPolicySafe(long policyId) throws PolicyNotFoundException {
    // Here is we hit our fallback we want to log a warning & simply act as if the policy wasn't found by throwing the same contingency exception as the API does
    LOGGER.warn("Falling back to circuit-breaker for getting policy {}", policyId);

    throw new PolicyNotFoundException(policyId);
  }
}

Answer 2

虽然您的解决方案可能对您有用，但我注意到您的代码中有一些奇怪之处（我无法检查我的假设，所以我想请您检查一下）。

1. 尽量避免在代码中使用检查异常，因为它是 难以维护。
2. 根据您的代码，您将永远无法捕捉到 “PolicyNotFoundException”，因为您使用 raiseHystrixExceptions = { HystrixException.RUNTIME_EXCEPTION } 这意味着您不会获得自定义异常，因此 HystrixRuntimeException 将被传播。尝试如下重写您的代码，以便它应该 简化代码，也许可以解决您的一些问题：

---

@Service
public class PolicyServiceImpl implements PolicyService {
  @HystrixCommand(groupKey = "PolicyService", fallbackMethod = "getPolicySafe")
  public Policy getPolicy(long policyId) throws PolicyNotFoundException {
    LOGGER.info("Getting policy {}", policyId);
    throw new PolicyNotFoundException(); // throw real PolicyNotFoundException if policy is absent for the given id
  }

  @HystrixCommand(groupKey = "PolicyService")
  private Policy getPolicySafe(long policyId) throws PolicyNotFoundException {
    // Here is we hit our fallback we want to log a warning & simply act as if the policy wasn't found by throwing the same contingency exception as the API does
    LOGGER.warn("Falling back to circuit-breaker for getting policy {}", policyId);

    throw new PolicyNotFoundException(policyId);
  }
}

Answer 3

这是 hystrix 的默认行为。 “如果命令有回退，那么只有触发回退逻辑的第一个异常才会传播给调用者”

请参阅错误传播部分here。

Answer 4

我这样做：

@Component
public class HystrixClient {

  @HystrixCommand(ignoreExceptions = {ClientArgumentException.class})
  public POJO getPojo(String id)
        throws ClientNoDataFoundException, ClientArgumentException, ClientGeneralException {

    //call my service and return POJO
  }
}

@Component
public TrueClientUsedForAnotherSerivce {

  @Autowired
  HystrixClient hystrixClient;

 public POJO getPojo(String id)
        throws ClientNoDataFoundException, ClientArgumentException, ClientGeneralException, ClientOpenCircuitException {
    try {           
        POJO result = hystrixClient.getCellular(id);            

        return result;
    }
    catch(HystrixRuntimeException e) {
        LOG.debug("The circuit is open");
        throw new ClientOpenCircuitException("Open circuit");
    }
}   

仅当@HystrixCommand 方法在另一个类中时才有效。