android - 尝试从 URL : Unable to resolve host "jsonplaceholder.typicode.com": No address associated with hostname 解析 JSON 数据

Question

我正在尝试从 URL 解析 JSON 数据并将其显示在 listView 中，但出现此错误:

03-27 20:53:04.830 13960-14086/com.example.samplejson E/HttpHandler: IOException: Unable to resolve host "jsonplaceholder.typicode.com": No address associated with hostname

03-27 20:53:04.830 13960-14086/com.example.samplejson E/MainActivity: Response from url: null

03-27 20:53:04.830 13960-14086/com.example.samplejson E/MainActivity: Couldn't get json from server.

我已经在我的 androidmanifest.xml 中添加了这一行:

<uses-permission android:name="android.permission.INTERNET" />

这是我的 MainActivity.java 文件:

public class MainActivity extends AppCompatActivity {
private String TAG = MainActivity.class.getSimpleName();

private ProgressDialog pDialog;
private ListView lv;

// URL to get contacts JSON
private static String url = "https://jsonplaceholder.typicode.com/users";

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.listview);

    new GetContacts().execute();
}

/**
 * Async task class to get json by making HTTP call
 */
private class GetContacts extends AsyncTask<Void, Void, Void> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Showing progress dialog
        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setMessage("Please wait...");
        pDialog.setCancelable(false);
        pDialog.show();

    }

    @Override
    protected Void doInBackground(Void... arg0) {
        HttpHandler sh = new HttpHandler();

        // Making a request to url and getting response
        String jsonStr = sh.makeServiceCall(url);

        Log.e(TAG, "Response from url: " + jsonStr);

        if (jsonStr != null) {
            try {


                // Getting JSON Array node
                JSONArray contacts = new JSONArray(jsonStr);

                // 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 username = c.getString("username");
                    String phone = c.getString("phone");

                   /* // 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("phone", phone);

                    // 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(Void result) {
        super.onPostExecute(result);
        // Dismiss the progress dialog
        if (pDialog.isShowing())
            pDialog.dismiss();
        /**
         * Updating parsed JSON data into ListView
         * */
        ListAdapter adapter = new SimpleAdapter(
                MainActivity.this, contactList,
                R.layout.item_list, new String[]{"nom", "email",
                "tel"}, new int[]{R.id.name,
                R.id.email, R.id.phone});

        lv.setAdapter(adapter);
    }

}
}

HttpHandler 类:

public class HttpHandler {

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

public HttpHandler() {
}

public 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();
}


}

有什么建议吗？

Answer 1

问题可能是由于没有可用的互联网连接而发生的。

因此，只需在您的设备(运行应用程序的地方)连接到互联网后重新验证。如果已关闭，请将其打开。

希望对您有所帮助。