Android Facebook SDK 4.X，如何获取电子邮件地址和Facebook访问令牌以将其传递到Web服务

fbLoginBtn.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {    @Override    public void onSuccess(LoginResult loginResult) {        GraphRequest.newMeRequest( loginResult.getAccessToken(), new GraphRequest.GraphJSonObjectCallback() {     @Override     public void onCompleted(JSonObject me, GraphResponse response) {         if (response.getError() != null) {  // handle error         } else {  String email = me.optString("email");  String id = me.optString("id");  // send email and id to your web server         }     } }).executeAsync();    }    @Override    public void onCancel() {        // App pre    }    @Override    public void onError(FacebookException exception) {        // App pre    }});