How to inject HttpServletRequest into a Spring AOP request (custom scenario)?

Question

I know the standard way of writing an AOP advice around a controller method and that you can get access to the HttpServletRequest arg, if declared in controller method.

But my scenario is that I have a translation service, that is currently session-scoped maintaining the user's locale for translation. I feel this makes the service stateful and also I do not want it to be session-scoped, as I think it is really Singleton. But there are multiple places where the translation service methods are called and so I do not want to change the signature to add request/locale in these methods. The problem is that all the callers of the translation service's methods do not have access to HttpServletRequest (not controller methods)? Can I write an aspect around the translation service methods and somehow magically get access to HttpServletRequest regardless of whether it is available in the caller's context or not?

@Service
public class TranslationService {
    public void translate(String key) {
        ...
    }
}

@Aspect
@Component
public class LocaleFinder {
    @PointCut("execution(* TranslationService.translate(..))")
    private void fetchLocale() {}

    @Around("fetchLocale()") // in parameter list
    public void advice(JoinPoint joinpoint, HttpServletRequest request) { .... } 
}

If now, the caller of translate does not have HttpServletRequest, can't I get request in the advice? Is there a workaround?

Answer 1

Can I write an aspect around the translation service methods and somehow magically get access to HttpServletRequest regardless of whether it is available in the caller's context or not?

Not easily. Actually, it would require a lot of effort.

The easy way to do it is to rely on RequestContextHolder. In every request, the DispatcherServlet binds the current HttpServletRequest to a static ThreadLocal object in the RequestContextHolder. You can retrieve it when executing within the same Thread with

HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.currentRequestAttributes()).getRequest();

You can do this in the advice() method and therefore don't need to declare a parameter.