model.addAttribute("method", "update");

@RequestMapping(method = RequestMethod.GET, value = "/update/{id}")
public String forUpdate(Model model, @PathVariable("id") Long id) {
    SystemRole systemRole = systemRoleService.getById(id);
    model.addAttribute("systemRole", systemRole);
    model.addAttribute("method", "update");
    return "role/role_edit";
}

model.addAttribute("method", "update");

原文：http://www.cnblogs.com/CESC4/p/7397031.html