jsp页面里的list确定为有值 报错： 没有为参数号1设置值

  <c:forEach var="as" items="${list}">
 <tr>

  <td><a href="ShowById?id=${as.id}" >${as.id}</a></td>
  <td>${as.name} </td>
  <td>${as.author}</td>
  <td>${as.publish}</td>
  <td>${as.pdate}</td>
  <td>${as.isbn}</td>
  <td>${as.page}</td>       

 </tr>
</c:forEach>  
 <tr>
    <td colspan="7" align="center"><input type="submit" value="提交"/></td>
 </tr>
</table>

<!-- 下面是ShowById的代码 这是一个servlet-->
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
int Id = Integer.parseInt( request.getParameter("id")) ;
Shop sp = new ShopDaoImpl().ShowAllById(Id);
System.out.println(Id);
request.setAttribute("sp",sp);
request.getRequestDispatcher("dds.jsp").forward(request, response);
}