在AsyncTask中的onExecute中请求数据

@Override
protected String doInBackground(String... strings) {
    try {
        URL url = new URL(strings[0]);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(6000);
        if (conn.getResponseCode() == HttpURLConnection.HTTP_OK){
            InputStream ins = conn.getInputStream();
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            int len = 0;
            byte[] buf = new byte[1024];
            while ((len = ins.read(buf)) > -1) {
                baos.write(buf, 0, len);
            }
            String msg = baos.toString();
            ins.close();
            baos.close();
            conn.disconnect();
            return msg;
        }
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

怎么报IOException: Cleartext HTTP traffic to www.imooc.com not permitted