Allow Spring MVC Controllers to control which fragment(s) to render for a composite view

Currently it is only possible to specify fragments client-side, which doesn't really mesh with MVC concepts and allows the client to render other views that should not be renderable for a given resource. Web Flow allows for controlling fragment rendering server-side, but Spring JavaScript's MVC integration does not. We should add support for this with Spring MVC.

Specification:
-
A MVC Controller can return a String viewname in the format [compositeViewName]#[fragment1,fragmentN].

Example:

@RequestMapping(value="/application/info", method = RequestMethod.POST)
public String processInfoSubmission(PersonalInfo personalInfo, BindingResult errors, AjaxHandler handler, Model model) {
personalInfo.validate(errors);
if (errors.hasErrors())

{ return "application#info"; }

contestantService.saveInfo(personalInfo);
if (handler.isAjaxRequest())

{ model.addAttribute("status", contestantService.getApplicationStatus()); return "application#status"; }

else

{ return "redirect:/application/info"; }

}

The example above says render the info fragment of the application composite when there are validation errors. Render the status fragment after successful submit and it's an ajax request.