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

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))
}

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)

As of Java 1.7 you all should be using java.nio. It offers close-to-native performance (java.io is very slow) and has some useful helpers

But Java 1.8 introduces exactly what you are looking for:

import java.nio.file.{FileSystems, Files}
import scala.collection.JavaConverters._
val dir = FileSystems.getDefault.getPath("/some/path/here") 

Files.walk(dir).iterator().asScala.filter(Files.isRegularFile(_)).foreach(println)

You also asked for file matching. Try java.nio.file.Files.find and also java.nio.file.Files.newDirectoryStream

See documentation here: http://docs.oracle.com/javase/tutorial/essential/io/walk.html

Tags:

Scala

Recent Posts