List only folders of certain depth using Java 8 streams

Question

Considering there is the "new" streams API in Java 8 I can use Files.walk to iterate over a folder. How can I only get the child folders of my given directory if using this method or maybe depth=2?

I currently have this working example, which sadly also prints the root path as all "subfolders".

Files.walk(Paths.get("/path/to/stuff/"))
     .forEach(f -> {
        if (Files.isDirectory(f)) {
            System.out.println(f.getName());
        }
     });

I therefore reverted to the following approach. Which stores the folders in memory and needs handling of the stored list afterwards, which I would avoid and use lambdas instead.

File[] directories = new File("/your/path/").listFiles(File::isDirectory);

May be count the number of backslash in the path in foreach loop and whatever having the depth as required can be filtered out — Aman Chhabra, Jul 26 '18 at 06:49
You could probably use [Files.walk with maxDepth](https://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#walk-java.nio.file.Path-int-java.nio.file.FileVisitOption...-) or [Files.walkTree with maxDepth](https://docs.oracle.com/javase/8/docs/api/java/nio/file/Files.html#walkFileTree-java.nio.file.Path-java.util.Set-int-java.nio.file.FileVisitor-) — Lino, Jul 26 '18 at 06:55

score 16 · Accepted Answer · answered Jul 26 '18 at 06:55

16

To list only sub-directories of a given directory:

Path dir = Paths.get("/path/to/stuff/");
Files.walk(dir, 1)
     .filter(p -> Files.isDirectory(p) && ! p.equals(dir))
     .forEach(p -> System.out.println(p.getFileName()));

answered Jul 26 '18 at 06:55

Andreas

154,647
11
152
247

Works like a charm! Thanks – lony Jul 26 '18 at 07:30
That only works for first depth. What if I want folders of depth 3 only? – L. Holanda Apr 05 '19 at 00:43

L. Holanda · Answer 2 · 2019-04-05T18:39:19.977

Here is a solution that works with arbitrary minDepth and maxDepth also larger than 1. Assuming minDepth >= 0 and minDepth <= maxDepth:

final int minDepth = 2;
final int maxDepth = 3;
final Path rootPath = Paths.get("/path/to/stuff/");
final int rootPathDepth = rootPath.getNameCount();
Files.walk(rootPath, maxDepth)
        .filter(e -> e.toFile().isDirectory())
        .filter(e -> e.getNameCount() - rootPathDepth >= minDepth)
        .forEach(System.out::println);

To accomplish what you asked originally in the question of listing "...only folders of certain depth...", just make sure minDepth == maxDepth.

This should be the accepted answer as it deals with min and max depths — FSm, Oct 06 '20 at 11:27

score 5 · Answer 3 · answered Jul 26 '18 at 09:02

5

You can make use of the second overload of the Files#walk method to set the max depth explicitly. Skip the first element of the stream to ignore the root path, then you can filter only directories to finally print each one of them.

final Path root = Paths.get("<your root path here>");

final int maxDepth = <your max depth here>;

Files.walk(root, maxDepth)
    .skip(1)
    .filter(Files::isDirectory)
    .map(Path::getFileName)
    .forEach(System.out::println);

answered Jul 26 '18 at 09:02

marsouf

1,107
8
15

1

1+ for using `.skip()` – FSm Oct 06 '20 at 11:50
voted for skip() – maruf571 Oct 07 '21 at 10:46

score 2 · Answer 4 · answered Feb 12 '20 at 13:25

2

public List<String> listFilesInDirectory(String dir, int depth) throws IOException {
    try (Stream<Path> stream = Files.walk(Paths.get(dir), depth)) {
        return stream
                .filter(file -> !Files.isDirectory(file))
                .map(Path::getFileName)
                .map(Path::toString)
                .collect(Collectors.toList());
    }
}

answered Feb 12 '20 at 13:25

ghandour abdelkrim

41
2

Welcome to Stack Overflow! Your answer would be considerably better if you were to add some explanatory text, as to how your code fixes the OP's problem(s). – Adrian Mole Feb 12 '20 at 13:50

score 0 · Answer 5 · answered Jul 26 '18 at 07:24

You can also try with this:

private File getSubdirectory(File file){
    try {
        return new File(file.getAbsolutePath().substring(file.getParent().length()));
    }catch (Exception ex){

    }
    return null;
}

collect file:

File[] directories = Arrays.stream(new File("/path/to/stuff")
          .listFiles(File::isDirectory)).map(Main::getSubdirectory)
                                        .toArray(File[]::new);

score 0 · Answer 6 · answered Jul 26 '18 at 07:34

0

Agree with Andreas‘s answer，u can also use Files.list instead of Files.walk

Files.list(Paths.get("/path/to/stuff/"))
.filter(p -> Files.isDirectory(p) && ! p.equals(dir))
.forEach(p -> System.out.println(p.getFileName()));

answered Jul 26 '18 at 07:34

kira

15
1

1

`Files.list` is not recursive so you're basically limited to the depth of 1 only. Does not answer the original question of "*only folders of **certain** depth*". – L. Holanda Apr 05 '19 at 18:43

List only folders of certain depth using Java 8 streams

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