“An error occured while executing doInBackground()” - android-external-storage

Question

i'm using the below code to get the file length and using which i display progress bar till i download the total file but i get an error from firebase crash report like below
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:304)
#Override
protected String doInBackground(String...Url) {
try {
URL url = new URL(Url[0]);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("HEAD");
connection.connect();
// Detect the file lenghth
fileLength = connection.getContentLength();
} else {
URLConnection connection = url.openConnection();
connection.connect();
// Detect the file lenghth
fileLength = connection.getContentLength();
}
/*
HttpURLConnection connection = (HttpURLConnection)url.openConnection();
connection.setRequestMethod("HEAD");
connection.connect();
int fileLength = connection.getContentLength();*/
// Locate storage location
// String filepath = Environment.getExternalStorageDirectory().getPath();
String filepath = getFilesDirectory(getApplicationContext()).getPath();
// File fo = getFilesDirectory(getApplicationContext());
// Download the file
InputStream input = new BufferedInputStream(url.openStream());
// Save the downloaded file
if (lang_slector == 0) {
// input stream to read file - with 8k buffer
File folder = new File(filepath, "/offlinedata/");
folder.mkdir();
File pdfFile = new File(folder, englishpdffilename);
try {
pdfFile.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
OutputStream output = new FileOutputStream(filepath + "/offlinedata/" +
pdffilename);
byte data[] = new byte[1024];
long total = 0;
int count;
while ((count = input.read(data)) != -1) {
total += count;
// Publish the progress
publishProgress((int)(total * 100 / fileLength));
output.write(data, 0, count);
}
// Close connection
output.flush();
output.close();
input.close();
} else if (lang_slector == 1) {
// input stream to read file - with 8k buffer
File folder = new File(filepath, "/offlinedata/");
folder.mkdir();
File pdfFile = new File(folder, englishpdffilename);
try {
pdfFile.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
OutputStream output = new FileOutputStream(filepath + "/offlinedata/" +
englishpdffilename);
byte data[] = new byte[1024];
long total = 0;
int count;
while ((count = input.read(data)) != -1) {
total += count;
// Publish the progress
publishProgress((int)(total * 100 / fileLength));
output.write(data, 0, count);
}
// Close connection
output.flush();
output.close();
input.close();
}
} catch (Exception e) {
// Error Log
Log.e("Error", e.getMessage());
e.printStackTrace();
}
return null;
}