US Passport holder: flying SFO to Narita with 24 layover in shanghai.

Do i need to get any kind of visa while here in the us before i travel this april? im flying china eastern airlines from SFO To shanghai, and then 24 hours later from Shanghai to Narita in japan. Japan at the moment doesnt require us citizens to hold a permit for tourist entry thats less than 90 days. ill be spending 9 days in japan and then flying back the same way i came. I dont want to encounter any visa problems the moment i arrive in PRC while waiting to catch my flight the next day to japan, This is my 1st time ever doing something like this. What do i need to do?