Problem with a shopping cart application using Stripes

[Alain Altet]

I'm trying to implement a simple shopping cart for an e-commerce site I'm building for my wife using Stripes (great framework, by the way), and everything is working fine so far, except for one thing: I can't update the quantity of a particular item once it's been added to the shopping cart.

I can hit the "Add to cart" link again and it will update the quantity, but I also want to be able to type in the exact quantity directly in the quantity field.

This is my shopping cart Action Bean:

public class ShoppingCartActionBean extends BaseActionBean
{
	private static final String SHOPPING_CART = "/WEB-INF/jsp/shopping_cart.jsp"; 
	private ShoppingCart shoppingCart = ShoppingCart.getInstance();
	private Product product;
	private List<Item> selectedItems = new ArrayList<Item>();
	
	@DefaultHandler
	public Resolution cart()
	{
		return new ForwardResolution(SHOPPING_CART);
	}

	public Resolution addToCart()
	{
		Item item = new Item(product);
		shoppingCart.addItem(item);
		return new ForwardResolution(SHOPPING_CART);
	}
	
	public Resolution updateCart()
	{
		for(Item i : selectedItems)
			shoppingCart.removeItem(i);

		return new ForwardResolution(SHOPPING_CART);
	}

	public Product getProduct()
	{
		return product;
	}
	
	public ShoppingCart getShoppingCart()
	{
		return shoppingCart;
	}

	@Validate(converter=ProductTypeConverter.class)
	public void setProduct(Product product)
	{
		this.product = product;
	}
	
	public List<Item> getSelectedItems()
	{
		return selectedItems;
	}

	@Validate(converter=ItemTypeConverter.class)
	public void setSelectedItems(List<Item> selectedItems)
	{
		this.selectedItems = selectedItems;
	}
}

and this is my shopping cart JSP:

<%@include file="/WEB-INF/jsp/common/taglibs.jsp" %>
<stripes:layout-render name="/WEB-INF/jsp/common/layout/layout_menu.jsp" pageTitle="Shopping Cart">
	<stripes:layout-component name="body">
		<c:choose>
			<c:when test="${empty actionBean.shoppingCart.items}">
				<div>Your shopping cart is empty.</div>
			</c:when>
			<c:otherwise>
				<table>
					<tr>
						<th>Product</th>
						<th>Quantity</th>
						<th>Price</th>
						<th>Sub-Total</th>
						<td>Remove Item</td>
					</tr>
					
					<stripes:form beanclass="com.tinycreations.action.ShoppingCartActionBean">
						<c:forEach var="item" items="${actionBean.shoppingCart.items}">
							<tr>
								<td>${item.name}</td>
								<td>${item.quantity}</td>
								<td>${item.price}</td>
								<td>${item.subTotal}</td>
								<td>
									<stripes:checkbox name="selectedItems" value="${item.product.id}" />
								</td>					
							</tr>
						</c:forEach>
						<tr>
							<td>
								<stripes:submit name="updateCart" value="Remove Selected Items" />
								<stripes:link beanclass="com.tinycreations.action.PlaceOrderActionBean" event="placeOrder">Place Order</stripes:link>
							</td>
						</tr>
					</stripes:form>					
					<tr>
						<th colspan="3">Total:</th>
						<td>${actionBean.shoppingCart.total}</td>
					</tr>
				</table>
			</c:otherwise>
		</c:choose>
	</stripes:layout-component>
</stripes:layout-render>

The form is populated by iterating thru the items in the cart. I have no problem removing a single item from the cart, but I have no idea how to reference a particular item in the cart (which I suppose is mandatory in order to be able to update said item). Anyone know how to achieve that?

By the way, I'm using a ShoppingCart class that implements a singleton pattern, so the shopping cart can be accessed from any action bean. I added this class as an extension to Stripes.

Thanks in advance!