Question

我使用HttpURLConnection来解析jsonResponse。它大部分时间都做得很好。但有时，它给出了java.lang.String java.lang.String.toString（）＆＃39;在此行中的空对象引用错误：＆＃34; jsonResponse = new JSONObject（response.toString（））;＆＃34;然后应用程序崩溃。我正在使用try并赶上这里，但应用程序崩溃了。为什么应用程序崩溃btw？我该如何解决这个问题？

错误日志

11-06 16:31:59.312 21887-21887/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.zzz.com.zz, PID: 21887
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.String.toString()' on a null object reference
   at com.zzz.com.zz.jobschedulers.MainActivity$LoginTask.onPostExecute(MainActivity.java:761)
   at com.zzz.com.zz.jobschedulers.MainActivity$LoginTask.onPostExecute(MainActivity.java:664)
   at android.os.AsyncTask.finish(AsyncTask.java:651)
   at android.os.AsyncTask.access$500(AsyncTask.java:180)
   at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
   at android.os.Handler.dispatchMessage(Handler.java:102)
   at android.os.Looper.loop(Looper.java:148)
   at android.app.ActivityThread.main(ActivityThread.java:7409)
   at java.lang.reflect.Method.invoke(Native Method)
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

码

class LoginTask extends AsyncTask<String, Void, String> {
    @Override
    protected void onPreExecute() {

    }

    protected String doInBackground(String... params) {
        URL url;
        String response = "";
        try {
            url = new URL("http://zzzz.com");

            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(25000);
            conn.setConnectTimeout(25000);
            conn.setRequestMethod("POST");
            conn.setDoInput(true);
            conn.setDoOutput(true);


            OutputStream os = conn.getOutputStream();
            BufferedWriter writer = new BufferedWriter(
                    new OutputStreamWriter(os, "UTF-8"));
            HashMap<String, String> h1 = new HashMap<String, String>();


            h1.put("username", email);
            h1.put("password", password);
            writer.write(getPostDataString(h1));

            writer.flush();
            writer.close();
            os.close();
            int responseCode = conn.getResponseCode();
            Log.e("upload gps", "uploaded");
            if (responseCode == HttpsURLConnection.HTTP_OK) {
                String line;
                BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                while ((line = br.readLine()) != null) {
                    response += line;
                }
                return response;
            } else {
                response = "";

            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }


    @Override
    protected void onPostExecute(String response) {

        JSONObject jsonResponse = null;
        try {
            jsonResponse = new JSONObject(response.toString());
            status = jsonResponse.getString("status");
            responseMsg = jsonResponse.getString("message");

            if (status.equalsIgnoreCase("true")) {
                Log.e("response ", response + "");

                JSONObject jsonResponse1 = jsonResponse.getJSONObject("data");
                String userId = jsonResponse1.getString("user_id");
                Log.e("userId", userId + "");
                if (userId != null) {
                    SharedPreferences abc = PreferenceManager.getDefaultSharedPreferences(MainActivity.this);
                    SharedPreferences.Editor editor2 = abc.edit();
                    editor2.putString("userId", userId);
                    editor2.apply();

                } else {
                }
                Intent i = new Intent(MainActivity.this, LiveTrack.class);
                i.putExtra("userId", userId);
                startActivity(i);

            } else {
                Log.e("response", "onloginfailed");
                validate();
                Toast.makeText(MainActivity.this, "Smth went wrong. Please check your network and try again", Toast.LENGTH_SHORT).show();
            }
        } catch (JSONException e) {
            Log.e("Json", "execption" + e);
        }
    }
}

private String getPostDataString(HashMap<String, String> params) throws UnsupportedEncodingException {
    StringBuilder result = new StringBuilder();
    boolean first = true;
    for (Map.Entry<String, String> entry : params.entrySet()) {
        if (first)
            first = false;
        else
            result.append("&");

        result.append(URLEncoder.encode(entry.getKey(), "UTF-8"));
        result.append("=");
        result.append(URLEncoder.encode(entry.getValue(), "UTF-8"));
    }

    return result.toString();
}

Answer 1

所以你的问题就是为什么即使你设置了Try / Catch它也会崩溃。所以我的答案是你已经捕获了JSONException异常，这与Json-Parsing相关。

所以请使用下面的Try / Catch。

JSONObject jsonResponse = null;
    try {
        jsonResponse = new JSONObject(response.toString());
        status = jsonResponse.getString("status");
        responseMsg = jsonResponse.getString("message");

        if (status.equalsIgnoreCase("true")) {
            Log.e("response ", response + "");

            JSONObject jsonResponse1 = jsonResponse.getJSONObject("data");
            String userId = jsonResponse1.getString("user_id");
            Log.e("userId", userId + "");
            if (userId != null) {
                SharedPreferences abc = PreferenceManager.getDefaultSharedPreferences(MainActivity.this);
                SharedPreferences.Editor editor2 = abc.edit();
                editor2.putString("userId", userId);
                editor2.apply();

            } else {
            }
            Intent i = new Intent(MainActivity.this, LiveTrack.class);
            i.putExtra("userId", userId);
            startActivity(i);

        } else {
            Log.e("response", "onloginfailed");
            validate();
            Toast.makeText(MainActivity.this, "Smth went wrong. Please check your network and try again", Toast.LENGTH_SHORT).show();
        }
    } catch (JSONException e) {
        Log.e("Json", "execption" + e);
    } catch (Exception e) {
        Log.e("Generic", "execption" + e);
    }

请注意，在上面我添加了一个带有通用Exception的Catch。希望这对你有用。

Answer 2

实际问题出在其他地方。您的onPostExecute(String result)执行以下操作：

jsonResponse = new JSONObject(response.toString());

然而，在您doInBackground()的最后，您明确表示：

return null;

doInBackground()应该返回一个结果（参见documentation）。您将返回null，因此在onPostExecute()中，如果连接失败，则始终执行此操作：

jsonResponse = new JSONObject(null.toString());

因此，您的应用程序崩溃，Android运行时抱怨您尝试在null上运行toString()。要解决此问题，您必须在String result

中返回所需的doInBackground()

Answer 3

onPostExecute()之前jsonResponse = new JSONObject(response.toString());上的

输入此内容：if(response == null)return;

toString方法给我空指针异常

3 个答案: