Java Programs›File Handling›List Files in a Directory

List Files in a Directory in Java

intermediate· File Handling · File I/O

Problem

A directory holds entries that are either files or subdirectories; listing it returns its direct children, while walking it descends into every subfolder.

Create a small folder with two files and a subfolder, then list its direct contents in alphabetical order, labelling each entry.

Input

demo-folder/ with readme.md, data.csv and images/

Output

[file] data.csv, [dir] images, [file] readme.md

Java Program

Java

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Comparator;
import java.util.stream.Stream;

public class ListFilesInDirectory {
    public static void main(String[] args) throws IOException {
        Path dir = Paths.get("demo-folder");
        Files.createDirectories(dir.resolve("images"));      // a subfolder
        Files.writeString(dir.resolve("readme.md"), "# Demo");
        Files.writeString(dir.resolve("data.csv"), "id,name");
        Files.writeString(dir.resolve("images").resolve("logo.png"), "png");

        try (Stream<Path> entries = Files.list(dir)) { // direct children only
            entries.sorted()                          // listing order isn't guaranteed, so sort it
                   .forEach(p -> System.out.println((Files.isDirectory(p) ? "[dir]  " : "[file] ") + p.getFileName()));
        }

        deleteTree(dir);
    }

    static void deleteTree(Path dir) throws IOException {
        try (Stream<Path> all = Files.walk(dir)) {
            all.sorted(Comparator.reverseOrder()) // children before their parent folder
               .forEach(p -> p.toFile().delete());
        }
    }
}

▶ Run Code

Output

[file] data.csv
[dir]  images
[file] readme.md

Core Logic

Files.list streams the folder's direct entries; sorting them makes the output predictable, since the file system returns them in no guaranteed order.

How It Works

1createDirectories and writeString build a sample folder to list.
2Files.list(dir) opens a stream of paths in try-with-resources.
3sorted() orders the paths alphabetically, and each is labelled [dir] or [file].
4deleteTree removes everything afterwards, deleting children before their parent folder.

logo.png sits inside images/, so it doesn't appear — Files.list only goes one level deep.

💡

Key Point: Deleting a folder that still has contents fails, which is why the cleanup sorts paths in reverse order before deleting.

Key Concepts

Files.list()Files.isDirectory()Stream.sorted()Files.walk()

Approach 2: Recursive Listing with Files.walk()

Java

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Comparator;
import java.util.stream.Stream;

public class ListFilesRecursive {
    public static void main(String[] args) throws IOException {
        Path dir = Paths.get("demo-folder");
        Files.createDirectories(dir.resolve("images"));
        Files.writeString(dir.resolve("readme.md"), "# Demo");
        Files.writeString(dir.resolve("data.csv"), "id,name");
        Files.writeString(dir.resolve("images").resolve("logo.png"), "png");

        try (Stream<Path> all = Files.walk(dir)) { // every level, starting with dir itself
            all.filter(Files::isRegularFile)
               .map(p -> dir.relativize(p).toString().replace('\\', '/')) // same separator on every OS
               .sorted()
               .forEach(System.out::println);
        }

        try (Stream<Path> all = Files.walk(dir)) {
            all.sorted(Comparator.reverseOrder()).forEach(p -> p.toFile().delete());
        }
    }
}

▶ Run Code

Output

data.csv
images/logo.png
readme.md

Core Logic

Files.walk visits the folder and everything beneath it, so nested files are included.

How It Works

1Files.walk(dir) streams every path at every depth.
2filter(Files::isRegularFile) keeps files and drops folders.
3dir.relativize(p) shows each path relative to the folder, with / as the separator on every OS.

images/logo.png now appears alongside the two top-level files.

💡

Key Point: Pass a depth limit, as in Files.walk(dir, 2), when scanning large directory trees, so the walk doesn't descend further than needed.