jsp弹窗并跳转

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setCharacterEncoding("GBK");
        String name = request.getParameter("textfield1");
        String pwd = request.getParameter("textfield2");
        String head = "<meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\" />";
        Sql sql = new Sql();
        PrintWriter out = response.getWriter();
        Connection conn = DbUtil.getConnection();
        try {
            PreparedStatement ps = conn.prepareStatement(sql.getInsert());
            PreparedStatement ps2 = conn.prepareStatement(sql.getSelect());
            ps.setObject(1,name);
            ps.setObject(2,pwd);
            ps2.setObject(1,name);
            ResultSet rs = ps2.executeQuery();
            if (rs.next()){
                response.getWriter().write("<script > alert(\"用户已经存在！请重新输入用户名！\");location='register.jsp';</script>");
            }else{
                ps.execute();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

### response.getWriter().write("<script > alert(\"用户已经存在！请重新输入用户名！\");location='register.jsp';</script>");