Nets Star Joe Johnson -- Dumping ATL Mansion After Trade to Brooklyn

Former Atlanta Hawks star Joe Johnson wasn't too attached to his GINORMOUS Georgia mansion -- TMZ has learned he listed the place for $4.7 mil after he was traded to the Brooklyn Nets.

Johnson purchased the massive 13,822 square-foot-pad back in 2005 for $3.8 mil -- the same year he signed with the Hawks. Fast forward to 2012 ... Johnson is traded to Brooklyn under a $119-million contract and it's sayonara GA.

The 7-bedroom, 9-bath crib is pretty AMAZING too ... 10-foot-high ceilings ...sleek modern decor ... movie theater ... massive game room ... infinity edge pool and spa. Plus, it sits on almost 2 acres of land.

Not gonna find that in Park Slope.