There seems to be four different Johnsons's Courts in Dublin city in 1848 (src: Thom's Directory) :
1. off Haddington Road, St. Peters (Civil Parish), 4 houses in tenements
2. off Basin Lane, St James, Tenements
3. off Great Brittan Street, St. George, 1-7 & 9 Tenements,
8,10, & 11 businesses
4. East Johnson's Court between Grafton Street and Clarendon St, St. Anne's
numbers 1-17
there is a listing for Denis on the last one :
13. Moran Dennis, chimney sweeper
he is next door to a Nailer and another Sweep
other businesses on the street at the time include :
bookseller, eating house, hairdresser, dairy, vintner
boarding house, book & shoe maker
Shane