由Hystrix回退引发的捕获异常？

Question

我正在设计一个服务外观，我有一个方法签名，看起来像这样：

public Policy getPolicy(long policyId) throws PolicyNotFoundException

如果没有不良事件发生，则返回一个Policy对象(简单POJO)。如果未找到请求的策略，则会抛出检查的异常PolicyNotFoundException (仅作为参考-当涉及到应用程序内的异常处理的最佳实践时，我们遵循this article )。

服务外观层(在本例中为Spring MVC RestController)之上的层知道如何处理这样的PolicyNotFoundException并返回适当的有效负载。

我正在尝试通过这样的方式将其合并到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，我想让我的断路器表现得就像原来的查找没有找到策略一样。然而，我遇到的问题是，我从回退方法中抛出的异常在翻译过程中迷失了方向。我最终在上面的层中看到的异常是command方法抛出的RuntimeException，而不是fallback方法抛出的异常。有什么办法可以解决这个问题吗？我也不想更改原始方法的契约，也不想让它上面的层知道在策略找不到的情况下必须捕获PolicyNotFoundException之外的任何事情。这里所需的任何内容都应该在此服务外观层中捕获。

任何帮助都将不胜感激。谢谢!

Answer 1

因此，基于@spencergibb给出的链接-我可能在升级到Hystrix 1.5.7之后找到了解决方案。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

这是hystrix的默认行为。“如果命令有回退，则只会将触发回退逻辑的第一个异常传播到调用方”

请参阅错误传播部分here。

Answer 3

虽然您的解决方案可能对您有效，但我注意到您的代码中有一些奇怪的地方(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，因为它很难维护。
2. 基于你的代码，你永远不会捕捉到"PolicyNotFoundException“，因为你使用的是raiseHystrixExceptions ={ HystrixException.RUNTIME_EXCEPTION }，这意味着你不会得到你的自定义异常，所以HystrixRuntimeException将被传播。试着重写你的代码，如下所示，这样就可以简化代码，也许还能修复一些问题：

@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);
  }
}