Easily read strings while tracking the number of bytes read?

Question

Hi all,
I'm after a way to easily parse and read strings from a file, while also being able to check (at any point) how many bytes have currently been read from that file.
I currently use the following for the string processing:
BufferedReader in = new BufferedReader(new FileReader(filename));
String str = null;
while ((str = in.readLine()) != null)
  // process the string
}That's all fine, but the files I'm reading can be very large (multi GB) so obviously it can take a while to read them. During this time I pop up a progress bar, and attempt to track the progress of the read. The files I'm working with just now come with a header on the first line that states how many "somethings" (that I happen to be looking for) will appear in the file. I can use that number to set the maximum value for the progress bar, and update its current value as I find them.
However... I'm also about to start working with files that don't contain this information. I've thought of two ways of knowing how much work has to be done in advance of the read so the maximum value for the progress bar can be set:
1) Quickly count the number of lines in the file without doing any processing. This works, but can still take some time for large files, even with more efficient reading algorithms.
2) Use File.length() to set the maximum to be the number of bytes that will read.
I'd like to use 2), but can't work out a way to use simple String based file parsing (as in the code above), but also be able to know how many bytes have been read so far. Using this code means I don't have to worry about end of line terminators, charset encoding, etc - the Reader does it for me.
Any suggestions?
Thanks

Answer 1

import javax.swing.*;
Component parent; // might be null, or your JFrame
String message; // message to display in the progress bar
BufferedReader br = new BufferedReader(new InputStreamReader(new ProgressMonitorInputStream(parent, message, new FileInputStream(file)), charset));