Kotlin Standard Library Cookbook

How it works...

We start by instantiating the File type instance that references the src/main/resources directory and invoking the walk() function on it. walk() returns the FileTreeWalk instance, which is a high-level abstraction layer over the filesystem and allows us to iterate through the files and subdirectories of the original File object.

FileTreeWalk extends a Sequence<File> interface and provides an Iterator<File> implementation, which allows us to iterate through the files and apply any transforming operations to them, in the same way we do while working with collections. 

Next, we apply a few filtering operations—removing the File objects referencing directories, removing files that don't contain the .txt extension, and removing ...