Hystrix fallback引发的捕获异常？

Question

我设计一个服务的门面，我有一个方法签名，看起来像这样：

public Policy getPolicy(long policyId) throws PolicyNotFoundException 

如果什么也没有发生，然后策略对象（PO​​JO简单）被返回。如果未找到所请求的策略，则会引发检查异常PolicyNotFoundException（仅作为参考 - 当涉及应用程序内异常处理的最佳实践时，我们会遵循this article）。

服务门面层上方的层（在本例中为Spring MVC RestController）知道如何处理此类PolicyNotFoundException并返回适当的有效内容。

我试图做这样的事情纳入到HystrixCommand这样的：

@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); 
} 

基本上我想要我的断路器简单地表现为，如果政策不是由原始的查询发现。我遇到的问题是，我从fallback方法抛出的异常在翻译的某处丢失。我在上面的图层中看到的异常是由命令方法抛出的RuntimeException，而不是fallback方法抛出的异常。有没有解决的办法？我不想更改原始方法的合同，也不希望上面的图层知道除了在未找到策略的情况下必须捕获PolicyNotFoundException之外的任何内容。无论这里需要什么，都应该在这个服务门面层中捕获。

任何和所有的帮助将不胜感激。谢谢！

Answer 1

这是hystrix的默认行为。 “如果命令有一个回退，那么只有第一个例外，即trigers fallback逻辑将传播给调用者”

请参见错误传播部分here。

Answer 2

因此基于@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 3

当你的解决方案可能会为你工作，我已经注意到你的代码中有些古怪（我无法检查我的假设，所以我想问一下你来检查一下）。

1. 尽量避免在代码中使用已检查的异常，因为它的 难以维护。
2. 根据您的代码，您将永远不会捕获 “PolicyNotFoundException”，因为您正在使用raiseHystrixExceptions = {HystrixException.RUNTIME_EXCEPTION}这意味着您将不会获取您的自定义异常，以便传播HystrixRuntimeException。尝试重写代码如下所以应该 简化代码，也许解决一些你的问题：

---

@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); 
    } 
}