ExceptionHandler doesn't work with Throwable

Question

Ours is a Spring MVC based REST application. I am trying to use ExceptionHandler annotation to handle all errors and exceptions.

I have

    @ExceptionHandler(Throwable.class)
    public @ResponseBody String handleErrors() {
        return "error";
    }

This works whenever there is an exception thrown and it doesn't work for any errors.

I am using Spring 4.0. Is there any work-around?

Answer 1

Contrary to what the ExceptionHandler#value() attribute indicates

Class<? extends Throwable>[] value() default {};

and @ExceptionHandler is only meant to handle Exception and its sub types.

Spring uses ExceptionHandlerExceptionResolver to resolve your annotated handlers, using the following method

doResolveHandlerMethodException(HttpServletRequest request,
        HttpServletResponse response, HandlerMethod handlerMethod, Exception exception) 

which as you can see only accepts an Exception.

You cannot handle Throwable or Error types with @ExceptionHandler with this configuration.

I would tell you to provide your own HandlerExceptionResolver implementation which does handle Throwable instances, but you'd need to provide your own DispatcherServlet (and most of the MVC stack) yourself since DispatcherServlet does not catch Throwable instances at any place where you could make any significant difference.

---

Update:

Since 4.3, Spring MVC wraps a thrown Throwable value in a NestedServletException instance and exposes that to the ExceptionHandlerExceptionResolver.

Answer 2

You can do a kind of Hacking to capture Error in Spring MVC. First, define an Interceptor like this :

public class ErrorHandlingInterceptor extends HandlerInterceptorAdapter {
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception
{
    super.afterCompletion(request, response, handler, ex);

    controller.handleError(ex.getCause(), request, response);
} }

Second, define a method in your controller like "handleError" method:

    ErrorResponse errorResponse = new ErrorResponse();
    errorResponse.setExceptionId(exceptionId);
    errorResponse.setErrorMsg(ex.toString());
    errorResponse.setServerStackTrace(serverStackTrace(ex));

    response.setStatus(responseCode);
    response.setContentType("application/json");

    ObjectWriter writer = mapper.writer().withDefaultPrettyPrinter();
    writer.writeValue(response.getOutputStream(), errorResponse);

Finally, config your interceptor in Spring configuration.

<mvc:interceptors>
    <bean class="ErrorHandlingInterceptor" />
</mvc:interceptors>

Code in DispatchServlet:

            catch (Exception ex) {
            Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
// This is where to handle Exception by Spring.
// If Error happens, it will go to catch Error statement 
// which will call afterCompletion method
            mv = processHandlerException(processedRequest, response, handler, ex);
            errorView = (mv != null);
        }

        // Did the handler return a view to render?
        if (mv != null && !mv.wasCleared()) {
            render(mv, processedRequest, response);
            if (errorView) {
                WebUtils.clearErrorRequestAttributes(request);
            }
        }
        else {
            if (logger.isDebugEnabled()) {
                logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
                        "': assuming HandlerAdapter completed request handling");
            }
        }

        // Trigger after-completion for successful outcome.
        triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
    }

    catch (Exception ex) {
        // Trigger after-completion for thrown exception.
        triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
        throw ex;
    }
    catch (Error err) {
        ServletException ex = new NestedServletException("Handler processing failed", err);
        // Trigger after-completion for thrown exception.
        triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
        throw ex;
    }