Java: Using nio Files.copy to Move Directory

Question

I am new to the nio class, and am having trouble moving a directory of files to a newly created directory.

I first create 2 directories with:

File sourceDir = new File(sourceDirStr); //this directory already exists
File destDir = new File(destDirectoryStr); //this is a new directory

I then try to copy the existing files into the new directory, using:

Path destPath = destDir.toPath();
for (int i = 0; i < sourceSize; i++) {
    Path sourcePath = sourceDir.listFiles()[i].toPath();
    Files.copy(sourcePath, destPath.resolve(sourcePath.getFileName()));
}

This throws the following error:

Exception in thread "main" java.nio.file.FileSystemException: destDir/Experiment.log: Not a directory

I know that destDir/Experiment.log is not an existing directory; it should be a new file as a result of the Files.copy operation. Could someone point out where my operation is going wrong? Thanks!

Sparse

Does destDir exist on the disk though? If not you might have to create it using File#mkdirs() first. – Mazonson

I've run destDir.exists(), which returns True. It almost sounds like it thinks destDir/Experiment.log should be a directory. Is that not the case, though? – Sparse

Answer 1

You need to use walkFileTree to copy directories. If you use Files.copy on a directory only an empty directory will be created.

Following code taken/adapted from http://codingjunkie.net/java-7-copy-move/

File src = new File("c:\\temp\\srctest");
File dest = new File("c:\\temp\\desttest");
Path srcPath = src.toPath();
Path destPath = dest.toPath();

Files.walkFileTree(srcPath, new CopyDirVisitor(srcPath, destPath, StandardCopyOption.REPLACE_EXISTING));

public static class CopyDirVisitor extends SimpleFileVisitor<Path>
{
    private final Path fromPath;
    private final Path toPath;
    private final CopyOption copyOption;

    public CopyDirVisitor(Path fromPath, Path toPath, CopyOption copyOption)
    {
        this.fromPath = fromPath;
        this.toPath = toPath;
        this.copyOption = copyOption;
    }

    @Override
    public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException
    {
        Path targetPath = toPath.resolve(fromPath.relativize(dir));
        if( !Files.exists(targetPath) )
        {
            Files.createDirectory(targetPath);
        }
        return FileVisitResult.CONTINUE;
    }

    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException
    {
        Files.copy(file, toPath.resolve(fromPath.relativize(file)), copyOption);
        return FileVisitResult.CONTINUE;
    }
}

Nagoya

Answer 2

Simply make the destination directory if it doesn't exist.

File sourceDir = new File(source); //this directory already exists
File destDir = new File(dest); //this is a new directory
destDir.mkdirs(); // make sure that the dest directory exists

Path destPath = destDir.toPath();
for (File sourceFile : sourceDir.listFiles()) {
    Path sourcePath = sourceFile.toPath();
    Files.copy(sourcePath, destPath.resolve(sourcePath.getFileName()));
}

Note that sourceDir.listFiles() will also return directories, which you will either want t recurse into, or ignore...

Oil

Thanks, but unfortunately this still throws the same error. I've even run destDir.exists(), which returns True. It almost sounds like it thinks destDir/Experiment.log should be a directory. Is that not the case, though? – Sparse

I ran the code on by side and it works, as long as there are no sub directories in the directory I am trying to copy... – Oil

The only difference I can think of is, I need to use for (int i = 0; i < trainingFilesSize; i++) { Path vectorPath = vectorDir.listFiles()[i].toPath(); because I'll be copying certain indices. This shouldn't make a difference, though, right? – Sparse

You're right ... it shouldn't make a difference. I am confused. – Oil

Answer 3

This is my solution for recursively moving a directory from source to target. It works like a charm.

public static void move(Path source, Path target) throws IOException {

    class FileMover extends SimpleFileVisitor<Path> {
        private Path source;
        private Path target;

        private FileMover(Path source, Path target) {
            this.source = source;
            this.target = target;
        }

        @Override
        public FileVisitResult visitFile(final Path file, final BasicFileAttributes attrs) throws IOException {
            Files.move(file, target.resolve(source.relativize(file)),
                StandardCopyOption.REPLACE_EXISTING);
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult preVisitDirectory(final Path dir, final BasicFileAttributes attrs) throws IOException {
            Path newDir = target.resolve(source.relativize(dir));
            try {
                Files.copy(dir, newDir,
                    StandardCopyOption.COPY_ATTRIBUTES,
                    StandardCopyOption.REPLACE_EXISTING);
            } catch (DirectoryNotEmptyException e) {
                // ignore and skip
            }
            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult postVisitDirectory(final Path dir, final IOException exc) throws IOException {
            Path newDir = target.resolve(source.relativize(dir));
            FileTime time = Files.getLastModifiedTime(dir);
            Files.setLastModifiedTime(newDir, time);
            Files.delete(dir);
            return FileVisitResult.CONTINUE;
        }
    }

    FileMover fm = new FileMover(source, target);
    EnumSet<FileVisitOption> opts = EnumSet.of(FileVisitOption.FOLLOW_LINKS);

    Files.walkFileTree(source, opts, Integer.MAX_VALUE, fm);
}

Allhallowmas

Answer 4

for (int i = 0; i < sourceSize; i++) {
    Path sourcePath = sourceDir.listFiles()[i].toPath();
    Files.copy(sourcePath, destPath.resolve(sourcePath.getFileName()));
}

This is very strange code. You have already got a file count from somewhere, in sourceSize, yet you are calling listFiles() for every iteration. I would have expected something more like this:

for (File file : sourceDir.listFiles()) {
    Path sourcePath = file.toPath();
    Files.copy(sourcePath, destPath.resolve(sourcePath.getFileName()));
}

Sicular

For reasons that fall outside the scope of this question, I need to use the int i = 0... format. It has to do with selecting random numbers, and passing off the index number. – Sparse

You've missed the point completely. That's not a reason to keep calling listFiles() on every iteration. You are running the risk of the directory changing between iterations, and of processing the same file twice. – Sicular