Splitting fixed width text file into columns

[Masa Ito]

I have large fixed width text files that I need to parse. I regex'd a file
that defines the columns - so I now have a large arraylist of column
headers and column widths.

I can read a line of the large text file, then loop through the arraylist
of column headers, doing some math to grab the substrings - but this is
going to be a sluggish way to do it. I am hoping others some tricks for
doing something like this?

Thanks!