Duration - 4 days?

Dear all,

My boyfriend and I (both Swiss citizens) would like to visit China in in May 2017. Before we come to China we are travelling around the world.
Right before China we are in Japan for approximately four weeks.

Is it possible to apply for a visa in Japan/Tokyo? How many days does the embassy need to prepare the visas? Our idea was that we apply in Tokyo when we arrive there. Is that possible?

Thank you and kind regards,
Livia