public boolean isExists(String userName) {
        boolean ie = false;
        int result = 0;
        sql = "select count(*) as result from t_user where [user_name] = ?";
        try {
            super.openConn();
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, userName);
            rs = pstmt.executeQuery();
            if(rs.next()){
                result = rs.getInt("result");
            }
            if(result > 0){
                ie = true;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            super.closeAll();
        }
        return ie;
    }