讀取服務器發送的數據時為空字符串

Question

我在使用此代碼時遇到麻煩。 應該從服務器的響應中填充變量結果，但是由於任何原因，它始終返回空字符串。

這是完整的代碼：

public class FragmentRally extends Fragment {

public FragmentRally() {
    // Required empty public constructor
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_fragment_rally, container, false);


    new AsyncFetch().execute();


    return rootView;
}


// CONNECTION_TIMEOUT and READ_TIMEOUT are in milliseconds
public static final int CONNECTION_TIMEOUT = 10000;
public static final int READ_TIMEOUT = 15000;
private RecyclerView vistaRallye;
private AdapterRallye adaptadorRallye;

private class AsyncFetch extends AsyncTask<String, String, String> {
    ProgressDialog pdLoading = new ProgressDialog(getActivity());
    HttpURLConnection conn;
    URL url = null;

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        //this method will be running on UI thread
        pdLoading.setMessage("\tCarregant...");
        pdLoading.setCancelable(false);
        pdLoading.show();

    }

    @Override
    protected String doInBackground(String... params) {
        try {

            // Enter URL address where your json file resides
            // Even you can make call to php file which returns json data
            url = new URL("http://www.rallyecat.esy.es/Obtenir_events.php");

        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return e.toString();
        }
        try {

            // Setup HttpURLConnection class to send and receive data from php and mysql
            conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(READ_TIMEOUT);
            conn.setConnectTimeout(CONNECTION_TIMEOUT);
            conn.setRequestMethod("GET");

            // setDoOutput to true as we recieve data from json file
            conn.setDoOutput(true);

        } catch (IOException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
            return e1.toString();
        }

        try {

            int response_code = conn.getResponseCode();

            // Check if successful connection made
            if (response_code == HttpURLConnection.HTTP_OK) {

                // Read data sent from server
                InputStream input = conn.getInputStream();
                BufferedReader reader = new BufferedReader(new InputStreamReader(input));
                StringBuilder result = new StringBuilder();
                String line;

                while ((line = reader.readLine()) != null) {
                    result.append(line);
                }

                // Pass data to onPostExecute method
                return (result.toString());

            } else {

                return ("No hi ha connexió a internet.");
            }

        } catch (IOException e) {
            e.printStackTrace();
            return e.toString();
        } finally {
            conn.disconnect();
        }


    }

    @Override
    protected void onPostExecute(String result) {

        //this method will be running on UI thread

        pdLoading.dismiss();
        List<DataRallye> data = new ArrayList<>();

        pdLoading.dismiss();
        try {
            JSONArray jArray = new JSONArray(result);

            // Extract data from json and store into ArrayList as class objects
            for (int i = 0; i < jArray.length(); i++) {
                JSONObject json_data = jArray.getJSONObject(i);
                DataRallye dadesrallye = new DataRallye();
                dadesrallye.RallyeNom = json_data.getString("nom");
                dadesrallye.RallyeTipus = json_data.getString("tipus");
                dadesrallye.RallyeDataI = json_data.getString("datai");
                dadesrallye.RallyeDataF = json_data.getString("dataf");
                dadesrallye.RallyeCiutat = json_data.getString("ciutat");
                dadesrallye.RallyeOrganitzacio = json_data.getString("organitzacio");
                dadesrallye.RallyeFoto = json_data.getString("foto");
                data.add(dadesrallye);
            }

            // Setup and Handover data to recyclerview
            vistaRallye = (RecyclerView) getView().findViewById(R.id.llistarallyes);
            adaptadorRallye = new AdapterRallye(getActivity(), data);
            vistaRallye.setAdapter(adaptadorRallye);
            vistaRallye.setLayoutManager(new LinearLayoutManager(getActivity()));

        } catch (JSONException e) {
            Toast.makeText(getActivity(), e.toString(), Toast.LENGTH_LONG).show();
        }

    }

}

}

問題出現在這里：

// Read data sent from server
                InputStream input = conn.getInputStream();
                BufferedReader reader = new BufferedReader(new InputStreamReader(input));
                StringBuilder result = new StringBuilder();
                String line;

                while ((line = reader.readLine()) != null) {
                    result.append(line);
                }

                // Pass data to onPostExecute method
                return (result.toString());

此變量RESULT傳遞到這里，在這里我進行JSON解析。 但由於為空，因此直接進入catch異常：

@Override
    protected void onPostExecute(String result) {

        //this method will be running on UI thread

        pdLoading.dismiss();
        List<DataRallye> data = new ArrayList<>();

        pdLoading.dismiss();
        try {
            JSONArray jArray = new JSONArray(result);

            // Extract data from json and store into ArrayList as class objects
            for (int i = 0; i < jArray.length(); i++) {
                JSONObject json_data = jArray.getJSONObject(i);
                DataRallye dadesrallye = new DataRallye();
                dadesrallye.RallyeNom = json_data.getString("nom");
                dadesrallye.RallyeTipus = json_data.getString("tipus");
                dadesrallye.RallyeDataI = json_data.getString("datai");
                dadesrallye.RallyeDataF = json_data.getString("dataf");
                dadesrallye.RallyeCiutat = json_data.getString("ciutat");
                dadesrallye.RallyeOrganitzacio = json_data.getString("organitzacio");
                dadesrallye.RallyeFoto = json_data.getString("foto");
                data.add(dadesrallye);
            }

            // Setup and Handover data to recyclerview
            vistaRallye = (RecyclerView) getView().findViewById(R.id.llistarallyes);
            adaptadorRallye = new AdapterRallye(getActivity(), data);
            vistaRallye.setAdapter(adaptadorRallye);
            vistaRallye.setLayoutManager(new LinearLayoutManager(getActivity()));

        } catch (JSONException e) {
            Toast.makeText(getActivity(), e.toString(), Toast.LENGTH_LONG).show();
        }

這是從我們網站上的PHP文件生成的JSON：

[{"id_rally":"1","nom":"45e rallye costa brava","tipus":"velocitat i regularitat","datai":"2017-06-20","dataf":"2017-06-22","ciutat":"Girona","organitzacio":"rallyclassics ","foto":"brava.png"},{"id_rally":"2","nom":"26e rallye igualada","tipus":"velocitat","datai":"2017-08-13","dataf":"2017-08-16","ciutat":"Igualada","organitzacio":"ecb org","foto":"igualada.png"}]

Answer 1

conn.setDoOutput(true);. 

刪除該行。 因為您不會將數據寫入輸出流。

result.append(line); 

那應該是

result.append(line) + "\n"; 

Answer 2

對於“獲取”連接設置

 conn.setDoOutput(false);

setDoOutput（true）用於POST和PUT請求。