Single or Multiple entry to China?

I will be travelling to Asia for 3 weeks, Oct-4-Oct 25.
I have a round trip booked from Canada to Shanghai, Oct.4-Oct.25.
I also have a round trip booked form Shanghai to Tokyo. Oct.18-Oct 24.

So after my trip to Tokyo I have to re-enter China to make my flight to Canada back home. Do i need to apply for 1 entry or 2 entries to China.

Thank You