button onclick无法跳转
<button onclick="javascript:window.location.href='ShoppingCarServlet?opt=2&&id=<%=shopCar.getId()%>'" class= "delete" >-</button>
<input value="<%=shopCar.getCount() %>" type="text" id="buynum" name="buynum">
<button onclick="javascript:window.location.href='ShoppingCarServlet?opt=4&&id=<%=shopCar.getId()%>'" class= "Add" >+</button>