Furthermore, there is BaseControllerAdvice, which is annotated with @ControllerAdvice as follows. ControllerAdvice is a specialized component that can handle the @ExceptionHandler, @InitBinder, and @ModelAttribute methods:

@ControllerAdvice
public class BaseControllerAdvice {

    private final UserService userService;

    public BaseControllerAdvice(UserService userService) {
        this.userService = userService;
    }

    @ExceptionHandler(NotFoundException.class)
    public String handledNotFoundException(NotFoundException e, Model 
    model) {
        model.addAttribute("status", 400);
        model.addAttribute("exception", e);

        return "common/error";
    }

The BaseControllerAdvice.handleNotFoundException method that is annotated with @ExceptionHandler will catch NotFoundException, which is as follows:

public class NotFoundException extends RuntimeException {

    public NotFoundException(String message) {
        super(message);
    }

    public NotFoundException(String message, Throwable cause) {
        super(message, cause);
    }
}

It will set the model properties status, exception and will eventually forward to the common/error.ftl page:

    @ExceptionHandler(Exception.class)
    public String handleException(Exception e, Model model) {
        model.addAttribute("status", 500);
        model.addAttribute("exception", e);

        return "common/error";
    }

Also, it has the handleException method to catch and handle all other Exception types, and to forward to common/error.ftl:

    @ModelAttribute
    public void addCommonAttributes(@AuthenticationPrincipal 
     UserDetails userDetails, Model model) {
        if (userDetails != null) {
            User user = 
      userService.getByUsername(userDetails.getUsername());
            model.addAttribute("user", user);
        }
      }
    }

Additionally, it has the addCommonAttributes method to add any common Model attributes, which needs to be sent as part of all controller returns. In this case, we send an @Model attribute user so that the logged-in username can be shown in the header. @ModelAttribute is invoked whenever there is a GET request to a controller.