Socialauth - OAuth library in Java
Socialauth provides support to authenticate users through external oAuth providers like Gmail, Hotmail, Yahoo, Twitter, Facebook, LinkedIn, Foursquare, MySpace, Salesforce, Yammer as well as through OpenID providers like myopenid.com. It could be easily integrated.
It supports Importing contacts from Google, Yahoo or Hotmail. Support for importing friends from Facebook, followers from Twitter and contacts from LinkedIn is available, but currently Facebook, Twitter and LinkedIn do not provide email addresses. UPDATE: Hotmail has stopped providing email addresses.