Can we throw an exception in fallback or fallbackFactory of #FeignClient - spring-cloud

Question

I'm use the #FeignClient and want to do some logic(like record the exception information) when Feign throw Exception and then reply the result to front end.
I noticed Feign will throw FeignException when connection fail or http status not expect.
So I defined a #ExceptionHandler to caught FeignException after the callback method was invoked.
#ExceptionHandler(value = FeignException.class)
#ResponseBody
public ResponseResult feignException(FeignException exception){
String message = exception.getMessage();
byte[] content = exception.content();
int status = exception.status();
if(content!=null){
String response=new String(content);
message=String.format("%s response message : %s",message,response);
}
log.warn("{} : {} , cause by : {}",exception.getClass().getSimpleName(),message,exception.getCause());
return ResponseResult.fail(HttpStatus.valueOf(status),String.format("9%s00",status),message);
But it can't caught when I set the callback or callbackFactory of #FeignClient.
#FeignClient(url = "${onboardingcase.uri}",name = "OnBoardingCaseService",
fallbackFactory = OnBoardingCaseServiceFallBack.class)
#Component
#Slf4j
public class OnBoardingCaseServiceFallBack implements FallbackFactory<OnBoardingCaseService> {
#Override
public OnBoardingCaseService create(Throwable throwable) {
return new OnBoardingCaseService() {
#Override
public OnBoardingCaseVo query(String coid) {
if(throwable instanceof FeignException){
throw (FeignException)throwable;
}
return null;
}
};
}
}
I noticed because hystrix took over this method.And will catch exception in HystrixInvocationHandler.
try {
Object fallback = HystrixInvocationHandler.this.fallbackFactory.create(this.getExecutionException());
Object result = ((Method)HystrixInvocationHandler.this.fallbackMethodMap.get(method)).invoke(fallback, args);
if (HystrixInvocationHandler.this.isReturnsHystrixCommand(method)) {
return ((HystrixCommand)result).execute();
} else if (HystrixInvocationHandler.this.isReturnsObservable(method)) {
return ((Observable)result).toBlocking().first();
} else if (HystrixInvocationHandler.this.isReturnsSingle(method)) {
return ((Single)result).toObservable().toBlocking().first();
} else if (HystrixInvocationHandler.this.isReturnsCompletable(method)) {
((Completable)result).await();
return null;
} else {
return HystrixInvocationHandler.this.isReturnsCompletableFuture(method) ? ((Future)result).get() : result;
}
} catch (IllegalAccessException var3) {
throw new AssertionError(var3);
} catch (ExecutionException | InvocationTargetException var4) {
throw new AssertionError(var4.getCause());
} catch (InterruptedException var5) {
Thread.currentThread().interrupt();
throw new AssertionError(var5.getCause());
}
So I want to know how can I throw an exception when I using callback / callbackFactory or there is another way to instead callbackFactory to do the "call back"?
Many Thanks

Answer 1

I found a solution to this problem.
public class OnBoardingCaseServiceFallBack implements FallbackFactory<OnBoardingCaseService> {
#Override
public OnBoardingCaseService create(Throwable throwable) {
return new OnBoardingCaseService() {
#Override
public OnBoardingCaseVo query(String coid) {
log.error("OnBoardingCaseService#query fallback , exception",throwable);
if(throwable instanceof FeignException){
throw (FeignException)throwable;
}
return null;
}
};
}
}
And then caught the HystrixRuntimeException and get the cause of exception in ExceptionHandler for get the realException that was wrapped by Hystrix.
#ExceptionHandler(value = HystrixRuntimeException.class)
#ResponseBody
public ResponseResult hystrixRuntimeException(HystrixRuntimeException exception){
Throwable fallbackException = exception.getFallbackException();
Throwable assertError = fallbackException.getCause();
Throwable realException = assertError.getCause();
if(realException instanceof FeignException){
FeignException feignException= (FeignException) realException;
String message = feignException.getMessage();
byte[] content = feignException.content();
int status = feignException.status();
if(content!=null){
String response=new String(content);
message=String.format("%s response message : %s",message,response);
}
return ResponseResult.fail(HttpStatus.valueOf(status),String.format("9%s00",status),message);
}
String message = exception.getMessage();
log.warn("{} : {} , cause by : {}",exception.getClass().getSimpleName(),message,exception.getCause());
return ResponseResult.fail(ResultCode.FAIL.httpStatus(),ResultCode.FAIL.code(),message);
}
But I don't think that's a good way~

Answer 2

I have never done this in fallback, I have implemented custom error decoder(“CustomFeignErrorDecoder”) class and extended feign.codec.ErrorDecoder, every time an error occurs it comes to this class.
In decode function throw a custom exception and catch it in the controller or service layer to show your message to the frontend.
Example:
#Component
public class CustomFeignErrorDecoder implements ErrorDecoder {
#Override
public Exception decode(String methodKey, Response response) {
throw new CustomFeignErrorDecoderException(methodKey +" response status "+ response.status() +" request "+ response.request()+ " method "+ response.request().httpMethod());
}
}