java的对象老是建立不成功

。。。

public class UpdateNumber
extends HttpServlet {
。。。

public void doGet(。。。) throws
ServletException, IOException {
response.setContentType(CONTENT_TYPE);
PrintWriter out = response.getWriter();
HttpSession session = request.getSession();
int id;
try {
id = Integer.parseInt(request.getParameter("CDID"));
}
catch (Exception ex) {
id = 1;
}
System.out.println("id是"+id);
User user = (User) session.getAttribute("LoginUser");
if (user == null) {
out.println("<script type=\"text/javascript\">");
out.println("alert(\"请先登录！\")");
out.println("window.open(\"Login.jsp\",\"_self\")");
out.println("</script>");
return;