How do I list all files in a subdirectory in scala?

Question

Is there a good "scala-esque" (I guess I mean functional) way of recursively listing files in a directory? What about matching a particular pattern?

For example recursively all files matching "a*.foo" in c:\temp.

Answer 1

Take a look at scala.tools.nsc.io

There are some very useful utilities there including deep listing functionality on the Directory class.

If I remember correctly this was highlighted (possibly contributed) by retronym and were seen as a stopgap before io gets a fresh and more complete implementation in the standard library.

Answer 2

Scala code typically uses Java classes for dealing with I/O, including reading directories. So you have to do something like:

import java.io.File
def recursiveListFiles(f: File): Array[File] = {
  val these = f.listFiles
  these ++ these.filter(_.isDirectory).flatMap(recursiveListFiles)
}

You could collect all the files and then filter using a regex:

myBigFileArray.filter(f => """.*\.html$""".r.findFirstIn(f.getName).isDefined)

Or you could incorporate the regex into the recursive search:

import scala.util.matching.Regex
def recursiveListFiles(f: File, r: Regex): Array[File] = {
  val these = f.listFiles
  val good = these.filter(f => r.findFirstIn(f.getName).isDefined)
  good ++ these.filter(_.isDirectory).flatMap(recursiveListFiles(_,r))
}

Answer 3

Scala is a multi-paradigm language. A good "scala-esque" way of iterating a directory would be to reuse an existing code!

I'd consider using commons-io a perfectly scala-esque way of iterating a directory. You can use some implicit conversions to make it easier. Like

import org.apache.commons.io.filefilter.IOFileFilter
implicit def newIOFileFilter (filter: File=>Boolean) = new IOFileFilter {
  def accept (file: File) = filter (file)
  def accept (dir: File, name: String) = filter (new java.io.File (dir, name))
}