Connecting flight in Dubai - need visa?

by Erno Kapp
(Sasolburg, South Africa)

Sir / Madam,
Do I need a transit visa if I only need to switch flights at the airport in Dubai, i.e. I will not leave the airport?
This is for connecting flights from Johannesburg to Beijing and I am a South African citizen. The departure and return flights are three months apart. If yes, how long does it take and can I arrange this online? Cost?
Kindly respond to ernoka@gmail.com
Thanks
Erno