Spring ExceptionHandler but for normal beans

Question

I have been able to successfully use @ExceptionHandler annonated methodsorg.springframework.web.bind.annotation.ExceptionHandler in Controller Classes in my Spring projects to handle exceptions thrown by spring @RestController

Working example:

@Validated
@RestController
@RequestMapping(value = UrlsProperties.API_PATH, produces = MediaType.APPLICATION_JSON, consumes = { MediaType.APPLICATION_JSON })
@Api(value = "MyController", description = "MyController processing and forwarding controller")
public class MyController  {

    private static Logger log = LogManager.getLogger(MyController.class);

    ...

    @JsonFormat
    @ExceptionHandler(MissingServletRequestParameterException.class)
    public ResponseMessage handleMissingParams(MissingServletRequestParameterException ex) {

        String name = ex.getParameterName();
        log.error(name + " parameter is missing");
        return new ResponseMessage(400, ex.getMessage());
    }
}

I am trying to achieve the same way of exception handling but for a normal bean, [ not a controller ]. Simply adding an @ExceptionHanlder annotated method did not seem to catch the exceptions thrown by that bean's methods.

My question is how to handle exceptions thrown by a bean by writing a method inside this bean?

What do you mean by "handle exceptions" when applied to normal beans? For example, if a bean is supposed to return some long, but throws an exception instead, how would you "handle" that in you exceptoin handler? — M. Prokhorov
I meant a bean as in: a class which is defined in spring context; like a @Component or @Service class. Classes by themselves do not return values, they have several methods each might return something. And in my case, several methods might throw the same kind of exception inside this bean class. If it was a @Controller bean, it works, otherwise, no. — aboudirawas
Ok, replace "bean" with "bean method call" in my original comment. Then again: what would you do in your exception handler if a bean method throws instead of returning a value? Do you want to hide the fact that it threw? What's the return value then? — M. Prokhorov
Some of it does sound like AOP's afterthrowing, I do admit. Maybe try doing that. — M. Prokhorov
Just to clarify: the afterthrowing is not an exception handler. It's an action that runs when exception is being thrown, but it doesn't allow any recovery, like a proper exception handler might. — M. Prokhorov

Kayaman Kayaman · Accepted Answer · 2019-09-12T09:33:45

@ExceptionHandler annotation is not for general exception handling. It's used in controllers to convert an exception into a proper HTTP response. It won't work for normal beans, because only controllers return a response.

If any code (doesn't need to be in a bean) throws an exception and you don't handle it, it would eventually propagate up to your controller's exception handler and it would be converted to a response. That would be poor design though, as you should handle exceptions as early as you can.

What you can do is create exceptions that are meant to be propagated to your exception handlers. Your code catches an exception, then re-throws it wrapped into your own exception (such as IllegalRequestException). The handler then returns an error code and details to the caller.

Spring ExceptionHandler but for normal beans

1 Answers