public void addFormVotingUser(int userId, int formId) throws ErrorAddingUserException {
        try {
            String q = "insert into ValidVoter values(?, ?);";
            PreparedStatement st = conn.prepareStatement(q);
            st.setInt(1, userId);
            st.setInt(2, formId);
            st.executeUpdate();
            conn.commit();
        } catch (SQLException e) {
            e.printStackTrace();
            try {
                conn.rollback();
            } catch(Exception e2) {
                e2.printStackTrace();
            }
            throw new ErrorAddingUserException();
        }
    }