can't immediately read downloaded text file

can't immediately read downloaded text file

i have an app that download a text file from the web to the app private
folder (/data/data/com.example.app)that have some data i need to read when
the file is downloaded .
in my app :
private class DownloadTextFile extends AsyncTask<String, Integer, String> {
@Override
protected String doInBackground(String... sUrl) {
// download text file
}
@Override
protected void onPreExecute() {
super.onPreExecute();
// read text file
}
when i try to read text file i got an file not found error but when i
close the app and reopen it the app reads the downloaded text file just
fine