How I create an error handler (404, 500…) in Spring Boot/MVC

You may try the following code:

@ControllerAdvice
public class ExceptionController {
    @ExceptionHandler(Exception.class)
    public ModelAndView handleError(HttpServletRequest request, Exception e)   {
        Logger.getLogger(getClass().getName()).log(Level.SEVERE, "Request: " + request.getRequestURL() + " raised " + e);
        return new ModelAndView("error");
    }

    @ExceptionHandler(NoHandlerFoundException.class)
    public ModelAndView handleError404(HttpServletRequest request, Exception e)   {
        Logger.getLogger(getClass().getName()).log(Level.SEVERE, "Request: " + request.getRequestURL() + " raised " + e);
        return new ModelAndView("404");
    }
}