HttpServletRequest get JSON POST data

I am HTTP POST-ing to URL http://laptop:8080/apollo/services/rpc?cmd=execute

with POST data

{ "jsondata" : "data" }

Http request has Content-Type of application/json; charset=UTF-8

How do I get the POST data (jsondata) from HttpServletRequest?

If I enumerate the request params, I can only see one param, which is "cmd", not the POST data.