Transit-Visa?

I'm a german student, currently staying in Japan.
On my way back from Tokyo to Germany, I will have to change the Airport from "Shanghai Hongqiao" to "Shanghai Pudong Intl.". I will stay for 6 hours in China (and of course have to leave the Airport)
I have heard, that it is not necessary to apply for it as long as I won't stay longer than 24 hours in China.
Is this Information correct?