params.put("client_id", Constants.FACEBOOK_APP_API_KEY);
params.put("client_secret", Constants.FACEBOOK_APP_API_SECRET);
params.put("grant_type", "fb_exchange_token");
params.put("fb_exchange_token", tokenString);
RawAPIResponse apiResponse = facebook.callGetAPI("/oauth/access_token", params);
String response = apiResponse.asString();
AccessToken newAccessToken = new AccessToken(response);
String newToken = newAccessToken.getToken();
if(newToken != null) {
User facebookUser = facebook.getMe();