Scala Cookbook

12.8. Listing Files in a Directory

Problem

You want to get a list of files that are in a directory, potentially limiting the list of files with a filtering algorithm.

Solution

Scala doesn’t offer any different methods for working with directories, so use the listFiles method of the Java File class. For instance, this method creates a list of all files in a directory:

def getListOfFiles(dir: String):List[File] = {
  val d = new File(dir)
  if (d.exists && d.isDirectory) {
    d.listFiles.filter(_.isFile).toList
  } else {
    List[File]()
  }
}

The REPL demonstrates how you can use this method:

scala> import java.io.File
import java.io.File

scala> val files = getListOfFiles("/tmp")
files: List[java.io.File] = List(/tmp/foo.log, /tmp/Files.scala.swp)

Note that if you’re sure that the file you’re given is a directory and it exists, you can shorten this method to just the following code:

def getListOfFiles(dir: File):List[File] =
  dir.listFiles.filter(_.isFile).toList

Discussion

If you want to limit the list of files that are returned based on their filename extension, in Java, you’d implement a FileFilter with an accept method to filter the filenames that are returned. In Scala, you can write the equivalent code without requiring a FileFilter. Assuming that the File you’re given represents a directory that is known to exist, the following method shows how to filter a set of files based on the filename extensions that should be returned:

import java.io.File

def getListOfFiles(dir: File, extensions: List[String ...