public User login(String username, String password) {
        String sql = "select * from u_user where username = ? and password = ?";
        ResultSet rs = JdbcUtils.executeQuery(sql, username, password);
        User user = null;
            try {
                if (rs.next()) {
                    user = new User();
                    user.setUsername(rs.getString("username"));
                    user.setPassword(rs.getString("password"));
                    user.setGrade(rs.getInt("grade"));
                    return user;
                }
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } finally {
                JdbcUtils.close(rs);
            }
        return user;
    }