These are few basic steps which will help you to integrate your java application with facebook using facebook graph api.

Steps :

1) Register your application at http://www.facebook.com/developers/
2) Facebook will return Consumer Key and Consumer Secret for your application.

3) Create a login action:

String facebookPermissions = FacebookPermissions

// Login Action
String callbackUrl = "ApplicationUrl/controller/action"
String facebookAuthorizeUrl = "https://graph.facebook.com/oauth/authorize?client_id=FacebookApiKey&redirect_uri=callbackUrl&scope=facebookPermissions"  //             
redirect(url: facebookAuthorizeUrl)

4) Create a callback action .

///  Call back action: Where the facebook will redirect after succesful authentication.
 
String authCode = parms.code
String facebookTokenUrl = "https://graph.facebook.com/oauth/access_token?client_id=FacebookApiKey&client_secret=FacebookSecretKey&code=${authCode}&redirect_uri=callbackUrl&scope=facebookPermissions"            
URL url = new URL(facebookTokenUrl)
String response = url.text
// Retrieve the access token from the response

6) Persist the access token for future use. The access token never expire until the user explicitly rejects the application from his settings.

Hope this helped!

Cheers!

Anshul Sharma