public String postAchievement(String userId, URL achievementURL) throws FacebookException {
        ensureAuthorizationEnabled();
        JSONObject json = post(buildEndpoint(userId, "achievements"),
                            new HttpParameter[] {new HttpParameter("achievement", achievementURL.toString())}
                          ).asJSONObject();
        try {
            return json.getString("id");
        } catch (JSONException jsone) {
            throw new FacebookException(jsone.getMessage(), jsone);
        }
    }