JQuery关于购物车的问题

这个是JQuery的代码。

 <script type="text/javascript">
$(function(){
 $("#quantity").keyup(function(){
  if(isNaN($(this).val()) || parseInt($(this).val())<1){
   $(this).val("1");
   $("#totalPrice").html($("#price").val());
   return;
  }
  var total = parseFloat($("#price").val())*parseInt($(this).val());
  $("#totalPrice").html(total.toFixed(2));
 })

})
/*商品数量+1*/
function numAdd(){
 var num_add = parseInt($("#quantity").val())+1;
 if($("#quantity").val()==""){
  num_add = 1;
 }
 $("#quantity").val(num_add);
 var total = parseFloat($("#price").val())*parseInt($("#quantity").val());
 $("#totalPrice").html(total.toFixed(2));
}
/*商品数量-1*/
function numDec(){
 var num_dec = parseInt($("#quantity").val())-1;
 if(num_dec<1){
  //购买数量必须大于或等于1
  alert("not lt 1");
 }else{
  $("#quantity").val(num_dec);
  var total = parseFloat($("#price").val())*parseInt($("#quantity").val());
  $("#totalPrice").html(total.toFixed(2));
 }
}
</script>

这个是JSP里面的代码

     for(int i=0;i<cartquantity;i++)
        {
            String cartproduct_id=productidlist.get(i).toString();
            GetsSingleInfoFromProduct gsifp=new GetsSingleInfoFromProduct();
            String cartproduct_name=gsifp.getSingleProductName(cartproduct_id);
            String cartproduct_type=gsifp.getSingleProductType(cartproduct_id);
            float cartproduct_price=Float.parseFloat(productpricelist.get(i).toString());
    %>
    <table cellpadding="0" cellspacing="0" class="gwc_tb2" id="tab">
        <tr>
            <td class="tb2_td2"><a href="Single-<%out.println(cartproduct_id);%>.jsp"><img src="images/<%out.println(cartproduct_id);%>.jpg"/></a></td>
            <td class="tb2_td3"><a href="Single-<%out.println(cartproduct_id);%>.jsp"><%out.println(cartproduct_name);%></a></td>
            <td class="tb1_td4"><%out.println(cartproduct_type);%></td>
            <td class="tb1_td5">
                <span  id="min" style=" width:20px; height:18px;border:1px solid #ccc;" onclick="numDec()"/>-</span>
                <input id="quantity" class="product_quentity" name="" type="text" value="1" style=" width:30px; text-align:center; border:1px solid #ccc;"/>
                <span  id="add" style="width:20px; height:18px;border:1px solid #ccc;" onclick="numAdd()"/>+</span>
            </td>
            <td class="tb1_td6"><input id="price" class="productprice" style="color:#ff5500;font-size:14px; font-weight:bold;" value="<%=cartproduct_price%>"></td>
            <td class="tb1_td7"><a href="#">删除</a></td>
        </tr>
    </table>
        <%} %>
    <table cellpadding="0" cellspacing="0" class="gwc_tb3" >
        <tr>
            <td class="tb3_td2">已选商品 <label id="shuliang" style="color:#ff5500;font-size:14px; font-weight:bold;"><%out.print(cartquantity);%></label> 件</td>
            <td class="tb3_td3">合计(不含运费):<span>￥</span><span style=" color:#ff5500;"><span id="totalPrice" style="color:#ff5500;font-size:14px; font-weight:bold;"></span></span></td>
            <td class="tb3_td4"><span id="jz1">结算</span><a href="#" style=" display:none;"  class="jz2" id="jz2">结算</a></td>
        </tr>
    </table>

问题是我现在只对查询出的第一条结果有作用，后来想到动态生成的话id重复了，但
使用class去求和的话还是有问题

id不能重复，用样式选择器，然后改为dom关系操作

 <table cellpadding="0" cellspacing="0" class="gwc_tb2" id="tab">
        <tr>
            <td class="tb2_td2"><a href="Single-<%out.println(cartproduct_id);%>.jsp"><img src="images/<%out.println(cartproduct_id);%>.jpg"/></a></td>
            <td class="tb2_td3"><a href="Single-<%out.println(cartproduct_id);%>.jsp"><%out.println(cartproduct_name);%></a></td>
            <td class="tb1_td4"><%out.println(cartproduct_type);%></td>
            <td class="tb1_td5">
                <span  id="min" style=" width:20px; height:18px;border:1px solid #ccc;" onclick="numDec(this)"/>-</span><!--传入DOM对象--->
                <input id="quantity" class="product_quentity" name="" type="text" value="1" style=" width:30px; text-align:center; border:1px solid #ccc;"/>
                <span  id="add" style="width:20px; height:18px;border:1px solid #ccc;" onclick="numAdd(this)"/>+</span><!--传入DOM对象--->
            </td

        <td class="tb1_td6"><input id="price" class="productprice" style="color:#ff5500;font-size:14px; font-weight:bold;" value="<%=cartproduct_price%>"></td>
        <td class="tb1_td7"><a href="#">删除</a></td>
    </tr>
</table>

  <script type="text/javascript">
         $(function () {
             $("input.product_quentity").keyup(function () {
                 var price = $(this).closest('table').find('input.productprice');//同个table的price控件
                 if (isNaN($(this).val()) || parseInt($(this).val()) < 1) {
                     $(this).val("1");
                     $("#totalPrice").html(price.val());
                     return;
                 }
                 var total = parseFloat(price.val()) * parseInt($(this).val());
                 $("#totalPrice").html(total.toFixed(2));
             })

         })
         /*商品数量+1*/
         function numAdd(o) {
             var quantity = $(o).closest('table').find('input.product_quentity'), price = $(this).closest('table').find('input.productprice'); ;
             var num_add = parseInt(quantity.val()) + 1;
             if (quantity.val() == "") {
                 num_add = 1;
             }
             quantity.val(num_add);
             var total = parseFloat(price.val()) * parseInt(quantity.val());
             $("#totalPrice").html(total.toFixed(2));
         }
         /*商品数量-1*/
         function numDec(o) {
             var quantity = $(o).closest('table').find('input.product_quentity'), price = $(this).closest('table').find('input.productprice'); ;
             var num_dec = parseInt(quantity.val()) - 1;
             if (num_dec < 1) {
                 //购买数量必须大于或等于1
                 alert("not lt 1");
             } else {
                 quantity.val(num_dec);
                 var total = parseFloat(price.val()) * parseInt(quantity.val());///////
                 $("#totalPrice").html(total.toFixed(2));
             }
         }
</script>