按照Android开发基础-网络编程(第一部分)P6处理请求到的数据编写的代码（稍有改动），不同之处是在fragment中进行的，问题出在给RecyclerView适配器传递数据时显示null object reference，从服务器得到的数据打印出来是对的，主要代码如下：

@Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        btn_send.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Log.d(TAG, "点击了按钮");
                sendResquestWithHttpURLConnection();
            }
        });
    }

    private void sendResquestWithHttpURLConnection() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                BufferedReader bufferedReader = null;
                try {
                    URL url = new URL("http://192.168.1.7:9102/get/text");
//                    URL url = new URL("https://api.sunofbeach.net/shop/api/discovery/categories");
                    connection = (HttpURLConnection) url.openConnection();
                    connection.setRequestMethod("GET");
                    connection.setConnectTimeout(8000);
                    connection.setReadTimeout(8000);
                    connection.connect();
                    Log.d(TAG, "开始连接");

                    int responseCode = connection.getResponseCode();
                    if (responseCode == 200) {
                        Map<String, List<String>> headerFields = connection.getHeaderFields();
                        Set<Map.Entry<String, List<String>>> entries = headerFields.entrySet();
                        for (Map.Entry<String, List<String>> entry : entries) {
                            System.out.println(entry.getKey() + " === " + entry.getValue());
                        }
                        InputStream inputStream = connection.getInputStream();

                        bufferedReader = new BufferedReader(new InputStreamReader(inputStream));

                        //在此处验证过bufferedReader 中的数据，无误

                        String json=bufferedReader.readLine();
                        Gson gson=new Gson();
                        GetTextItem getTextItem= gson.fromJson(json,GetTextItem.class);
                        updateUI(getTextItem);
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (bufferedReader != null) {
                        try {
                            bufferedReader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (connection != null) {
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }

    private void updateUI(final GetTextItem getTextItem) {
        getActivity().runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Log.d(TAG, "准备刷新UI");
                mAdapter.setData(getTextItem);             //bug定位在这里，与视频的区别主要在于GetTextItem多了final修饰，没法去掉
            }
        });
    }