public ModelAndView handleRequest(HttpServletRequest request,

        HttpServletResponse response) throws Exception {

    Member member = (Member) RequestUtil.parseRequestToObject(request,Member.class);

    if (member == null) {

        jzLogic.insertMember(member);

        return new ModelAndView("index");

    } else {

        return new ModelAndView("Error", "message", "账号已被注册！");

    }

}  

......

    response.setContentType("text/html; charset=gbk");

    PrintWriter out = response.getWriter();

    out.println("<script language='javascript'>");

    out.println("alert('账号已被注册！');");

    out.println("history.back();");

    out.print("</script>");

    return null;

......