How to get user Authenticated and get the request token and OAuth token

Hi,
i was trying to get Oauth authentication by following the Document https://platform.fatsecret.com/api/Default.aspx?screen=rapiauth
i am not able to do it using GET or POST method  using all valid parameter ?
its giving unExpected error .
is there a way through which we can get the OAuth using Java library ?
i have to get data frmo fat secret for a particular user .