Just do a redirect after post. After a form submission is successful, when returning your ModelAndView make sure the View is a RedirectView. From the user's POV, they submit the form, and then are redirected to make a "GET" to another URL. This way they won't double submit.
Note that when using a Redirect View, Model Attributes get exposed in the URL as the parameters. So you might want to keep the attributes as thin as possible. What I typically do is show the user a page that doesn't really contain any unique information, just a "confirm" message.