After successful login, you need to call following code. You can find user ID in the logged-in user details response.
Session session = Session.getActiveSession(); Request request = Request.newGraphPathRequest(session, "me", null); com.facebook.Response response = Request.executeAndWait(request)

After successful login, you need to call following code. You can get the logged-in user details with id in response.
Session session = Session.getActiveSession(); Request request = Request.newGraphPathRequest(session, "me", null); com.facebook.Response response = Request.executeAndWait(request)