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

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.

Solution 1:

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))
}

Solution 2:

I would prefer solution with Streams because you can iterate over infinite file system(Streams are lazy evaluated collections)

import scala.collection.JavaConversions._

def getFileTree(f: File): Stream[File] =
        f #:: (if (f.isDirectory) f.listFiles().toStream.flatMap(getFileTree) 
               else Stream.empty)

Example for searching

getFileTree(new File("c:\\main_dir")).filter(_.getName.endsWith(".scala")).foreach(println)