If concerned about 'how to catch it', I think lots of publications are on the internet to answer that. Would i drink my beer if someone let a drop of blood into it, yuk, the thought of it. Would it put you at risk if someone did maliciously? Don't know, but if you had tooth gum damage or other open mouth blister, chances may not be absolute zero.

Realising you are in China, there is web filtering, thus not sure if this information would even come thru. Here's a fact sheet from the USCDC: http://www.cdc.gov/hiv/pubs/facts/transmission.htm

The Misinformation sheet: http://psychology.ucdavis.edu/rainbow/html/stigma_02_contact.html

Here an answer on a FAQ website:

Hello Alex_8216,
I am not a professional so this is only a private opinion. Many more people would have AIDS if it were that easily transmitted. So the odds are a million to one in your favor.

The cheap way to check is to donate blood to a service that checks blood donations for HIV and tells the donor if they detect it.

Lawrence