public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception {
CartActionForm cartForm = (CartActionForm) form;
Cart cart = cartForm.getCart();
String workingItemId = cartForm.getWorkingItemId();
if (cart.containsItemId(workingItemId)) {
cart.incrementQuantityByItemId(workingItemId);
}
else {
// isInStock is a "real-time" property that must be updated
// every time an item is added to the cart, even if other
// item details are cached.