I am building a simple web applications with 3 layers - DAO, Service, MVC. When in my Controller I want to delete menu group and it contains menus I am getting ConstraintViolationException. Where should I handle this exception? In DAO, Service, or in Controller? Currently I am handling the exception in Controller. My code below. DAO method for deleting menu groups: @Override public void delete(E e){ if (e == null){ throw new DaoException("Entity can't be null."); } getCurrentSession().delete(e); } Service method for deleting menu groups: @Override @Transactional(readOnly = false) public void delete(MenuGroupEntity menuGroupEntity) { menuGroupDao.delete(menuGroupEntity); } Controller method for deleting menu groups in Controller: @RequestMapping(value = "/{menuGroupId}/delete", method = RequestMethod.GET) public ModelAndView delete(@PathVariable Long menuGroupId, RedirectAttributes redirectAttributes){ MenuGroupEntity menuGroupEntity = menuGroupService.find(menuGroupId); if (menuGroupEntity != null){ try { menuGroupService.delete(menuGroupEntity); redirectAttributes.addFlashAttribute("flashMessage", "admin.menu-group-deleted"); redirectAttributes.addFlashAttribute("flashMessageType", "success"); } catch (Exception e){ redirectAttributes.addFlashAttribute("flashMessage", "admin.menu-group-could-not-be-deleted"); redirectAttributes.addFlashAttribute("flashMessageType", "danger"); } } return new ModelAndView("redirect:/admin/menu-group"); }