My contract want to receive transfer with memo in json format, is there any libraries supporting the json parse?
There is no build-in json-parser in the libs provided by eosio.cdt but you could include one of the several lightweight json-libraries yourself.
I would advise against it because it's probably very CPU-intensive (and RAM-intensive to include such a lib) and you should see if you can find another, more useful way.
You can for example see here how Eos-Knights goes about it: Eos-Knights eosiotoken_transfer
