Spring MVC validators by default gives you a commandClass object which you can validate. For each variable in the commandClass there is a binding on jsp, which populates the variable. Now there may be some elements on your view which are not bound to any variable in the commandClass but you will still need to validate them. These elements will be available in HttpServletRequest as parameters.
So now the actual question - How will you get these parameters in the validator class and validate the unbound elements of your view?