我在代码运行时遇到此错误＆＃34;字符串无法转换为jsonobject＆＃34;

Question

我在代码运行时遇到此错误＆＃34;字符串无法转换为JSON对象

这是我的代码：

这些错误在android监视器中显示：来自url：null的响应，  来自网址：标签

的回复

Mainactivity：

public class MainActivity extends AppCompatActivity {

    private String TAG = MainActivity.class.getSimpleName();
    private ListView lv;

    ArrayList<HashMap<String, String>> contactList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        contactList = new ArrayList<>();
        lv = (ListView) findViewById(R.id.list);

        new GetContacts().execute();
    }

    private class GetContacts extends AsyncTask<String, String, String> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            Toast.makeText(MainActivity.this,"Json Data is downloading",Toast.LENGTH_LONG).show();

        }

        @Override
        protected String doInBackground(String... arg0) {
            HttpHandler sh = new HttpHandler();
            // Making a request to url and getting response
            String url = "http://api.androidhive.info/contacts/";
            String jsonString = sh.makeServiceCall(url);

            Log.e(TAG, "Response from url: " + jsonString);
            if (jsonString != null) {
                try {
                    JSONObject jsonObject = new JSONObject(jsonString);

                    // Getting JSON Array node
                    JSONArray contacts = jsonObject.getJSONArray("contacts");

                    // looping through All Contacts
                    for (int i = 0; i < contacts.length(); i++) {
                        JSONObject c = contacts.getJSONObject(i);
                        String id = c.getString("id");
                        String name = c.getString("name");
                        String email = c.getString("email");
                        String address = c.getString("address");
                        String gender = c.getString("gender");

                        // Phone node is JSON Object
                        JSONObject phone = c.getJSONObject("phone");
                        String mobile = phone.getString("mobile");
                        String home = phone.getString("home");
                        String office = phone.getString("office");

                        // tmp hash map for single contact
                        HashMap<String, String> contact = new HashMap<>();

                        // adding each child node to HashMap key => value
                        contact.put("id", id);
                        contact.put("name", name);
                        contact.put("email", email);
                        contact.put("address",address);
                        contact.put("mobile", mobile);
                        contact.put("home",home);


                        // adding contact to contact list
                        contactList.add(contact);
                    }
                } catch (final JSONException e) {
                    Log.e(TAG, "Json parsing error: " + e.getMessage());
                    runOnUiThread(new Runnable() {
                        @Override
                        public  void run() {
                            Toast.makeText(getApplicationContext(),
                                    "Json parsing error: " + e.getMessage(),
                                    Toast.LENGTH_LONG).show();
                        }
                    });

                }

            } else {
                Log.e(TAG, "Couldn't get json from server.");
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getApplicationContext(),
                                "Couldn't get json from server. Check LogCat for possible errors!",
                                Toast.LENGTH_LONG).show();
                    }
                });
            }

            return null;
        }

        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);
            ListAdapter adapter = new SimpleAdapter(MainActivity.this, contactList,
                    R.layout.list_item, new String[]{ "name","mobile","home","email","address",},
                    new int[]{R.id.name, R.id.mobile,R.id.home,R.id.email,R.id.address});
            lv.setAdapter(adapter);
        }
    }
}

HttpHandler.java：

class HttpHandler {

    private static final String TAG = HttpHandler.class.getSimpleName();

    HttpHandler() {
    }

    String makeServiceCall(String reqUrl) {
        String response = null;
        try {
            URL url = new URL(reqUrl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            // read the response
            InputStream in = new BufferedInputStream(conn.getInputStream());
            response = convertStreamToString(in);
        } catch (MalformedURLException e) {
            Log.e(TAG, "MalformedURLException: " + e.getMessage());
        } catch (ProtocolException e) {
            Log.e(TAG, "ProtocolException: " + e.getMessage());
        } catch (IOException e) {
            Log.e(TAG, "IOException: " + e.getMessage());
        } catch (Exception e) {
            Log.e(TAG, "Exception: " + e.getMessage());
        }
        return response;
    }

    private String convertStreamToString(InputStream is) {
        BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();

        String line;
        try {
            while ((line = reader.readLine()) != null) {
                sb.append(line).append('\n');
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        return sb.toString();
    }
}