Traverse a directory to list files in Kotlin

This post will discuss how to traverse a directory to “recursively” list all files in Kotlin.

There are several ways to traverse a directory and list out all files present in it (and its subdirectories):

1. Using `Files.walk()` function

The Files.walk() function takes the root directory and returns a Stream<Path> by walking the file tree recursively in a depth-first manner. After getting the Stream, you can apply a filter on it to list only regular files.

import java.nio.file.Files

import java.nio.file.Paths

fun main() {

val dir = "/var/www/html"

Files.walk(Paths.get(dir))

.filter { Files.isRegularFile(it) }

.forEach { println(it) }

}

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The above code fails to close the stream’s open directories after the stream’s operations have been completed. This function must be used within a use control structure to ensure that all resources are closed promptly. Here’s how the code would look like:

import java.nio.file.Files

import java.nio.file.Paths

fun main() {

val dir = "/var/www/html"

Files.walk(Paths.get(dir)).use {

paths -> paths.filter { Files.isRegularFile(it) }

.forEach { println(it) }

}

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Here’s an equivalent solution using the Files.find() function, which walks the file tree similar to the Files.walk() function.

import java.nio.file.Files

import java.nio.file.Paths

import java.nio.file.attribute.BasicFileAttributes

import java.util.function.BiPredicate

fun main() {

val dir = "/var/www/html"

Files.find(

Paths.get(dir), Int.MAX_VALUE,

BiPredicate { _, file: BasicFileAttributes -> file.isRegularFile }

).use { paths -> paths.forEach { println(it) } }

}

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2. Using `Files.walkFileTree()` function

Alternatively, you can use the Files.walkFileTree() function to walk a file tree. It requires the root directory and an instance of the file visitor to invoke for each file.

import java.nio.file.*

import java.nio.file.attribute.BasicFileAttributes

fun main() {

val dir = "/var/www/html"

Files.walkFileTree(Paths.get(dir), object : SimpleFileVisitor<Path>() {

override fun visitFile(path: Path, attributes: BasicFileAttributes): FileVisitResult {

println(path)

return FileVisitResult.CONTINUE

}

})

}

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That’s all about traversing a directory to recursively list all files in Kotlin.

Traverse a directory to list files in Kotlin

1. Using Files.walk() function

2. Using Files.walkFileTree() function

1. Using `Files.walk()` function

2. Using `Files.walkFileTree()` function