Get a list of files that are in a directory and subdirectories

getListOfFiles.scala

def recursiveListFiles(f: File): ArraySeq[File] = {
  val these = f.listFiles
  ArraySeq.from(these ++ these.filter(_.isDirectory).flatMap(recursiveListFiles))
}

///

import java.io.File
def getListOfFiles(dir: String): List[File] = {
  def go(dir: File): List[File] = dir match {
    case d if d.exists && d.isDirectory && d.canRead=>
      val files = d.listFiles.filter(a => a.canRead && a.isFile).toList
      val dirs  = dir.listFiles.filter(_.isDirectory).toList
      files ::: dirs.foldLeft(List.empty[File])(_ ::: go(_))
    case _ => List.empty[File]
  }
  go(new File(dir))
}

// using cats

import java.io.File
import cats.effect.IO
def getListOfFiles(dir: String): IO[List[File]] = {
  def go(dir: File): List[File] = dir match {
    case d if d.exists && d.isDirectory =>
      if (d.canRead) {
        val files = d.listFiles.filter(_.isFile).toList
        val dirs  = dir.listFiles.filter(_.isDirectory).toList
        files ::: dirs.foldLeft(List.empty[File])(_ ::: go(_))
      } else throw new IOException(s"Error opening directory '$d': Permission denied")
    case _ => List.empty[File]
  }
  IO.fromTry(Try(go(new File(dir))))
}