@RequestMapping(params = "action=add") // action phase
public void populateSite(
@ModelAttribute("site") PetSite petSite, BindingResult result, SessionStatus status, ActionResponse response) {
new PetSiteValidator().validate(petSite, result);
if (!result.hasErrors()) {
this.petSites.put(petSite.getName(), petSite.getUrl());
status.setComplete();
response.setRenderParameter("action", "list");
}