Java how to convert List of File objects to List of Path objects?

Question

I am building a library for which the user already has code that processes an array of Paths. I have this:

Collection<File> filesT = FileUtils.listFiles(
            new File(dir), new RegexFileFilter(".txt$"), 
            DirectoryFileFilter.DIRECTORY
          );

I use the List of File object throughout but needed a way to convert filesT to List<Path>. Is there a quick way, maybe lambda to quickly convert one list to the other?

And how did you mean to create a Path object from a File object? — Joakim Danielson
– Joakim Danielson, Commented Oct 13, 2020 at 20:14
To be clear, is the conversion from java.io.File to java.nio.file.Path? — John Kugelman
– John Kugelman, Commented Oct 13, 2020 at 20:16
Possibly related: Get java.nio.file.Path object from java.io.File — Pshemo
– Pshemo, Commented Oct 13, 2020 at 20:16
Why don’t you use Path in the first place? Getting a filtered list, including pattern matching, is already provided by the API. — Holger
– Holger, Commented Oct 14, 2020 at 11:22

Nowhere Man · Accepted Answer · 2020-10-14 12:57:48Z

3

If you have a Collection<File>, you can convert it to List<Path> or to Path[] using File::toPath method reference:

public List<Path> filesToPathList(Collection<File> files) {
    return files.stream().map(File::toPath).collect(Collectors.toList());
}

public Path[] filesToPathArray(Collection<File> files) {
    return files.stream().map(File::toPath).toArray(Path[]::new);
}

edited Oct 14, 2020 at 12:57

answered Oct 13, 2020 at 21:22

Nowhere Man

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1 Comment

Mike Over a year ago

Sorry late response but this is how I did what I needed to do. I actually used Jim Newpower's Set<Path> type from above. So technically you both have the answer. Thank guys.

Jim Newpower · Accepted Answer · 2020-10-13 22:01:42Z

2

I agree with Alex Rudenko's answer, however the toArray() would require a cast. I present an alternative (how I would implement, returning immutable collections):

Set<Path> mapFilesToPaths(Collection<File> files) {
    return files.stream().map(File::toPath).collect(Collectors.toUnmodifiableSet());
}

answered Oct 13, 2020 at 22:01

Jim Newpower

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