Java Library for authentication, getting profile, contacts and updating status on Google, Yahoo, Facebook, Twitter, LinkedIn, and many more providers
SocialAuth is a Java library (.NET port & Android version available) for you if your web application requires:
Authenticating 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.
Easy user registration. All you need to do is create a page where users can click on buttons for the above providers or other supported providers. Just call SocialAuth and you can get all their profile details.
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.