java.net.MalformedURLException：找不到协议：null

Question

这是我的MainActivity.java

/** AsyncTask to parse json data and load ListView */
    private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{

        JSONObject jObject;
        // Doing the parsing of xml data in a non-ui thread
        @Override
        protected SimpleAdapter doInBackground(String... strJson) {
            try{
                jObject = new JSONObject(strJson[0]);
                StoreJSONParser countryJsonParser = new StoreJSONParser();
                countryJsonParser.parse(jObject);
            }catch(Exception e){
                Log.d("JSON Exception1",e.toString());
            }

            // Instantiating json parser class
            StoreJSONParser countryJsonParser = new StoreJSONParser();

            // A list object to store the parsed countries list
            List<HashMap<String, Object>> countries = null;

            try{
                // Getting the parsed data as a List construct
                countries = countryJsonParser.parse(jObject);
            }catch(Exception e){
                Log.d("Exception",e.toString());
            }

            // Keys used in Hashmap
            String[] from = { "country","flag","details"};

            // Ids of views in listview_layout
            int[] to = { R.id.storename,R.id.icon};

            // Instantiating an adapter to store each items
            // R.layout.listview_layout defines the layout of each item
            SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), countries, R.layout.restaurant_list, from, to);

            return adapter;
        }

        /** Invoked by the Android on "doInBackground" is executed */
        @Override
        protected void onPostExecute(SimpleAdapter adapter) {

            // Setting adapter for the listview
            mListView.setAdapter(adapter);

            for(int i=0;i<adapter.getCount();i++){
                HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(i);
                String imgUrl = (String) hm.get("flag_path");
                ImageLoaderTask imageLoaderTask = new ImageLoaderTask();

                HashMap<String, Object> hmDownload = new HashMap<String, Object>();
                hm.put("flag_path",imgUrl);
                hm.put("position", i);

                // Starting ImageLoaderTask to download and populate image in the listview
                imageLoaderTask.execute(hm);
            }
        }
    }

    /** AsyncTask to download and load an image in ListView */
    private class ImageLoaderTask extends AsyncTask<HashMap<String, Object>, Void, HashMap<String, Object>>{

        @Override
        protected HashMap<String, Object> doInBackground(HashMap<String, Object>... hm) {

            InputStream iStream=null;
            String imgUrl = (String) hm[0].get("flag_path");
            int position = (Integer) hm[0].get("position");

            URL url;
            try {
                url = new URL(imgUrl);

                // Creating an http connection to communicate with url
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

                // Connecting to url
                urlConnection.connect();

                // Reading data from url
                iStream = urlConnection.getInputStream();

                // Getting Caching directory
                File cacheDirectory = getBaseContext().getCacheDir();

                // Temporary file to store the downloaded image
                File tmpFile = new File(cacheDirectory.getPath() + "/wpta_"+position+".png");

                // The FileOutputStream to the temporary file
                FileOutputStream fOutStream = new FileOutputStream(tmpFile);

                // Creating a bitmap from the downloaded inputstream
                Bitmap b = BitmapFactory.decodeStream(iStream);

                // Writing the bitmap to the temporary file as png file
                b.compress(Bitmap.CompressFormat.PNG,100, fOutStream);

                // Flush the FileOutputStream
                fOutStream.flush();

                //Close the FileOutputStream
                fOutStream.close();

                // Create a hashmap object to store image path and its position in the listview
                HashMap<String, Object> hmBitmap = new HashMap<String, Object>();

                // Storing the path to the temporary image file
                hmBitmap.put("flag",tmpFile.getPath());

                // Storing the position of the image in the listview
                hmBitmap.put("position",position);

                // Returning the HashMap object containing the image path and position
                return hmBitmap;

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

这是我的JSONParserClass.java

public class StoreJSONParser {
    // Receives a JSONObject and returns a list
    public List<HashMap<String,Object>> parse(JSONObject jObject){

        JSONArray jCountries = null;
        try {
            // Retrieves all the elements in the 'countries' array
            jCountries = jObject.getJSONArray("storelistfood");
        } catch (JSONException e) {
            e.printStackTrace();
        }

        // Invoking getCountries with the array of json object
        // where each json object represent a country
        return getCountries(jCountries);
    }

    private List<HashMap<String, Object>> getCountries(JSONArray jCountries){
        int countryCount = jCountries.length();
        List<HashMap<String, Object>> countryList = new ArrayList<HashMap<String,Object>>();
        HashMap<String, Object> country = null;

        // Taking each country, parses and adds to list object
        for(int i=0; i<countryCount;i++){
            try {
                // Call getCountry with country JSON object to parse the country
                country = getCountry((JSONObject)jCountries.get(i));
                countryList.add(country);

            } catch (JSONException e) {
                e.printStackTrace();
            }
        }

        return countryList;
    }

    // Parsing the Country JSON object
    private HashMap<String, Object> getCountry(JSONObject jCountry){

        HashMap<String, Object> country = new HashMap<String, Object>();
        String countryName = "";
        String flag="";
        /*String language = "";
        String capital = "";
        String currencyCode = "";
        String currencyName = "";*/

        try {
            countryName = jCountry.getString("STORENAME");
            flag = jCountry.getString("logo");
            /*language = jCountry.getString("language");
            capital = jCountry.getString("capital");
            currencyCode = jCountry.getJSONObject("currency").getString("code");
            currencyName = jCountry.getJSONObject("currency").getString("currencyname");*/

            /*String details =        "Language : " + language + "\n"; +
                    "Capital : " + capital + "\n" +
                    "Currency : " + currencyName + "(" + currencyCode + ")";*/

            country.put("country", countryName);
            country.put("flag", R.drawable.ninety_six);
            country.put("flag_path", flag);
            //country.put("details", details);

        } catch (JSONException e) {
            e.printStackTrace();
        }
        return country;
    }
}

这是logcat的错误

java.net.MalformedURLException: Protocol not found: null

此行url = new URL(imgUrl);以及private class ImageLoaderTask

我正在尝试使用JSON在listview中加载图像。我很确定我的数据库中的url是有效的。就像这样http://wptrafficanalyzer.in//p//demo1//india.png