Is this simple DAO approach sufficient?

[Rick]

I understanding I'm bind my DAOs to a particular sqlmap config being
loaded, but other than some 'purist' unit testing issues, what's wrong
with this simple approach (I'll have a couple different base DAOs that
will load a different config file because going against a different
DB.)



public abstract class GuiDAO  {
    public static final SqlMapClient sqlMap =
DaoUtil.loadSqlMapClient("sqlMapConfig-gui.xml");
}


public class UserDAO extends GuiDAO {
    private static UserDAO instance = new UserDAO();
    private UserDAO(){}
    public static UserDAO getInstance() {
        return instance;
    }

    public User getUserByDmzID(String dmzID) throws SQLException {
        return (User)sqlMap.queryForObject("User.getUserByDmzID", dmzID );
    }
                //...
}


Other daos that need a different db will extend a different parent DAO.

What are the big drawback to this?