Section 42I. Before revoking any license issued under section forty-two A, the commissioner shall give the licensee ten days’ notice, by delivery in hand or by mail, of the time and place of a hearing to determine whether or not such license shall be revoked. At such hearing, the commissioner or his duly authorized assistant shall receive evidence under oath and give the licensee an opportunity to be heard, and shall thereafter file an order either dismissing the proceeding or revoking such license. The decision of the commissioner following such hearing shall be final.