获得数据库自动产生主键

 psmt = conn.prepareStatement(str,Statement.RETURN_GENERATED_KEYS );
    psmt.setInt(1, 0);
    psmt.setInt(2, pid);  //这里父类的id号是1;
    psmt.setString(3, forumsForm.getF_name());
    psmt.executeUpdate();
    ResultSet rs2 = psmt.getGeneratedKeys();
    rs2.next();
    int fid = rs2.getInt(1); //获得自动产生的f_id号,以便直接记录到另一张forums_admin表f_id这一列中