class ProgressTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... path) {
        String content;
        try {
            content = getContent(path[0]);
        } catch (IOException ex) {
            content = ex.getMessage();
        }
        return content;
    }

    @Override
    protected void onPostExecute(String content) { //метод для получения ответа
        if (content.equals("server_connect")){
            Intent intent = new Intent(MainActivity.this, MainCl.class);
            startActivity(intent);
        } else {
            Toast.makeText(getApplicationContext(),R.string.server_error, Toast.LENGTH_LONG).show();
        }
        pb.setVisibility(View.INVISIBLE);
        btn.setText(R.string.next);
        btn.setEnabled(true);
    }

    private String getContent(String path) throws IOException {
        BufferedReader reader = null;
        try {
            URL url = new URL(path);
            HttpsURLConnection c = (HttpsURLConnection) url.openConnection();
            c.setRequestMethod("GET");
            c.setReadTimeout(PublicVar.time);
            c.connect();
            reader = new BufferedReader(new InputStreamReader(c.getInputStream()));
            StringBuilder buf = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                buf.append(line);
            }
            return (buf.toString());
        } finally {
            if (reader != null) {
                reader.close();
            }
        }
    }
}