这个问题在这里已经有答案了：

什么是nullpointerexception，如何修复它(12个答案）
两年前关门了。

@Override
protected Void doInBackground(String... strings) {
    String JSPN_Request = "";
    String response = "";
    URL url = null;
    JSONObject jsonObject = null;
    HttpURLConnection conn = null;
    OutputStream outputStream = null;
    OutputStreamWriter outputStreamWriter = null;
    BufferedWriter bufferedWriter = null;
    try
    {
        url = new URL(strings[0]);
        jsonObject = new JSONObject();
        jsonObject.put("userId",102);
        jsonObject.put("id",102);
        jsonObject.put("title","hello world");
        jsonObject.put("body","hello world");

        conn = (HttpURLConnection) url.openConnection();
        conn.setDoOutput(true);
        OutputStream os = conn.getOutputStream();
        outputStreamWriter = new OutputStreamWriter(os);
        bufferedWriter = new BufferedWriter(outputStreamWriter);
        bufferedWriter.write(jsonObject.toString());
        bufferedWriter.flush();
        bufferedWriter.close();
        outputStream.close();
        conn.setDoInput(true);
        BufferedReader reader = new BufferedReader(new
            InputStreamReader(conn.getInputStream()));
        StringBuilder sb = new StringBuilder();
        String line = null;
        while((line = reader.readLine()) != null) {
            sb.append(line);
            break;
        }
        reader.close();
        response = sb.toString().toString();

    }catch (Exception e)
    {
        Log.d(TAG, "----------------------------------json-error----------------------------------");
        Log.d(TAG, "POSTING ERROR" + e);
        Log.d(TAG, "----------------------------------json-error----------------------------------");
    }}

当我试图发布到数据库，我得到这个错误，我搜索了很多，但什么也没有。我正在使用localhost通过url（10.0.3.0:8000/post）发布这些数据，因为我正在使用genymotion模拟器。