Servlet - JSP Programming

Hi,

I'm writing a jsp page as shown below. I have to buttons of type submit. Any time only one is selected(either add to cart or checkout). I'm programming in a servlet getting the input parameters. But when i try the command request.getparameter to know which submit button is clicked, I'm getting an error. I found that, if i click the "add to cart" button it is showing error with "checkout" parameter and viceversa. The starting of my servlet code is also pasted below. please let me know how to solve it.



<form method="post" action="updateCart">

<table border="1">
<tbody>
<tr>
<td><input type="checkbox" name="chair" value="chair"></td>
<td>Chair</td>
<td>$10</td>
<td><input type="text" name="chair1" size="5"></td>
</tr>
<tr>
<td><input type="checkbox" name="table" value="table"></td>
<td>Table</td>
<td>$20</td>
<td><input type="text" name="table1" size="5"></td>
</tr>
<tr>
<td><input type="checkbox" name="lamp" value="lamp"></td>
<td>Lamp</td>
<td>$30</td>
<td><input type="text" name="lamp1" size="5"></td>
</tr>
</tbody>
</table>
<p><input type="submit" name="add_to_cart" value="Add2Cart"> <input
type="submit" name="checkout" value="checkout"></p>
<p><br></p>
<p></p>
</form>


SERVLET CODE
--------------------------
1)String add_to_cart = null;
2)String checkout = null;

3)add_to_cart=request.getParameter("add_to_cart").toString();

4)checkout = request.getParameter("checkout").toString();

5)if (add_to_cart.equals("Add2Cart")){


......

If i click add to cart button error is with line 4. if i click checkout error is with line 3.