Passing object from @ControllerAdvice to @Controller in Spring MVC

I want to check if user exists in ControllerAdvice and treat user as @ModelAttribute if user exists. On the other hand, I also want to access user object in @Controller directly. So I add @ModelAttribute annotation on the parameter of @RequestMapping method.

I'm using @ControllerAdvice like:

@ControllerAdvice
public class UserAdvice {

    @Autowired
    private UserService userService;

    @ModelAttribute("user")
    public User user(@PathVariable("username") String username) {
        User user = userService.findByUsername(username);
        if (user != null) {
            return user;
        }
        user = userService.findById(username);
        if (user == null) {
            throw new ResourceNotFoundException("user not found");
        }

        return user;
    }
}

And UserController Like:

@RestController
@RequestMapping("/users/{username}")
public class UserController {

    public static final Logger logger = LoggerFactory.getLogger(UserCourseListController.class);

    @Autowired
    private CourseService courseService;

    @RequestMapping(value = "", method = RequestMethod.GET)
    public void getUser(@ModelAttribute("user") User user, Model model) {
        logger.info("{}", user);//user is null
        logger.info("{}", model.asMap().get("user"));// not null
    }

}

But now, the parameter user that annotated with @ModelAttribute is null while there is a "user" obj in Model Map.

Is there any mistakes I've made in this scenario? Or any misunderstanding of the concepts of @ModelAttribute and @ControllerAdvice?

Thanks very much!

Update

From Docs of Springframework:

Once present in the model, the argument’s fields should be populated from all request parameters that have matching names.

So We cannot add @ModelAttribute to method parameters annotated by @RequestMapping directly because Spring will do data binding from request(not Model)。

Finally I found a solution——HandlerMethodArgumentResolver. It can resolve method arguments on each @RequestMapping method and do some work on resolving arguments. An example of Java Config is below:

public class Config extends WebMvcConfigurerAdapter {

    @Bean(name = "auditorBean")
    public AuditorAware<User> auditorAwareBean() {
        return () -> null;
    }

    @Bean
    public HttpMessageConverters customConverters() {
        return new HttpMessageConverters(new MappingJackson2HttpMessageConverter());
    }

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
        argumentResolvers.add(new HandlerMethodArgumentResolver() {
            @Override
            public boolean supportsParameter(MethodParameter parameter) {
                return parameter.getParameterType().equals(User.class);
            }

            @Override
            public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
                return mavContainer.getDefaultModel().get(parameter.getParameterName());
            }
        });
    }

}

We resolve method arguments from model via parameter.getParameterName(). It mean that the name of method argument(user) must be equal to the value of @ModelAttrubute defined in @ControllerAdvice. You can also use any other naming conventions to implement the binding.