You have a file hierarchy and you'd like to iterate over all the files and do something to them. I've accidentally solved this problem twice now and I figured I'd make a note if it so I don't do so again.
The first time I did it (and the solution I like better other than requiring an external library) is: org.himinbi.util.AntFileList. It simply wraps Ant's FileSet in an iterator. This allows you to specify complex sets of including and excluding patterns.
The second time was entierly with the standard library: org.himinbi.util.FileList. This is a lazy iterator and only gets the contents of a directory when necessary. It should be about as fast as possible.