public void close()     
    {
        try
        {
            if (stmt != null) 
            {
                stmt.close();
                stmt = null;
            }
            if (prepstmt != null) 
            {
                prepstmt.close();
                prepstmt = null;
            }
            conn.close();
            conn = null;
        }catch(Exception e){
            e.printStackTrace();
        }
    }