Single or Double?

Hi! I'm doing a trip from Australia to Japan, then to China, but can't quite work out how many numbers of entries this is categorised as.

First, I'm flying from Australia to Tokyo, transiting in Shanghai for 3 hours. Two weeks later I will be flying from Tokyo to Nanjing, transiting in Shanghai again for 4 hours.

With the flight back to Australia, I will depart from Nanjing, once again transiting in Shanghai for 12 hours. Do I need a double-entry visa? Or is single-entry sufficient as other times I'm merely transiting and don't intend to leave the airport.