In order to get the 72h VISA free, what have I to do?

Dear,
I bought the following flights (all with Air China):
- 13/10/2015 Milan 21.00 --> Beijing (PEK) 13.30 +1
- 17/10/2015 Beijing (PEK) 9.25 --> Narita 13.55
- 24/10/2015 Osaka 13.30 --> Shanghai (PVG) 14.55
- 27/10/2015 Shanghai (PVG) 1.30 --> Milan 7.15

As you can see I will stay less than 72h in Beijing and Shanghai, so I don't need the L type.

Have I to apply an online application before the trip? Will I get the free transit directly at the airport after landing? Have I to communicate to Air China at the check in that I need 72h free transit?
Many thanks
Regards