How to make a Stream from a DirectoryStream

Question

When reading the API for DirectoryStream I miss a lot of functions. First of all it suggests using a for loop to go from stream to List. And I miss the fact that it a DirectoryStream is not a Stream.

How can I make a Stream<Path> from a DirectoryStream in Java 8?

Answer 1

While it is possible to convert a DirectoryStream into a Stream using its spliterator method, there is no reason to do so. Just create a Stream<Path> in the first place.

E.g., instead of calling Files.newDirectoryStream(Path) just call Files.list(Path).

The overload of newDirectoryStream which accepts an additional Filter may be replaced by Files.list(Path).filter(Predicate) and there are additional operations like Files.find and Files.walk returning a Stream<Path>, however, I did not find a replacement for the case you want to use the “glob pattern”. That seems to be the only case where translating a DirectoryStream into a Stream might be useful (I prefer using regular expressions anyway)…

Answer 2

DirectoryStream is not a Stream (it's been there since Java 7, before the streams api was introduced in Java 8) but it implements the Iterable<Path> interface so you could write:

try (DirectoryStream<Path> ds = ...) {
  Stream<Path> s = StreamSupport.stream(ds.spliterator(), false);
}

Answer 3

DirectoryStream has a method that returns a spliterator. So just do:

Stream<Path> stream = StreamSupport.stream(myDirectoryStream.spliterator(), false);

You might want to see this question, which is basically what your problem reduces to: How to create a Stream from an Iterable.