The Form bean can do your basic validation. You can also use JavaScript but
you should always think of JavaScript as a bonus. Never rely on the JavaScript having sent valid data since the user can copy the page and edit out the JavaScript if he really wants to. JavaScript should be a convenience to the user not the programmer.
If you don't want to write a Form bean for every JSP, then you can use the DyanActionForm to do basic validation.
Remember, the form should be doing only basic validation. There should be no database reads or complex business logic.