public static List<User> selectAllusers(){
        try {
            Connection con = DB.getConnection();
            PreparedStatement s = con.prepareStatement(GETALLUSERS);
            ResultSet res = s.executeQuery();
            List<User> users = new ArrayList<User>(); 
            while(res.next()){
                users.add(extractUser(res));
            }        
            return users;
        } catch(Exception e){ }
        return null;
    }