new AsyncTask<Void, Void, Void>() {

            @Override
            protected Void doInBackground(Void... voids) {
                try {
                    URL url = new URL("http://YOUR_URL_HERE");
                    int fileLength = url.openConnection().getContentLength();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                return null;
            }
        }