ListFiles performance vs file system visitor

[Alan Bateman]

Paulo Levi wrote:
> Hi. I saw recently that the nio2 was going to have a new visitor like
> implementation for filesystem walking 
Yes, the method you want is Files#walkFileTree. It's not really possible 
to do recursive operations effectively with java.io.File today, esp. 
when there are symbolic links.

> and i am wondering if is faster
> than doing a recursive list files by hand. I'm my application this is
> the main bottleneck.
>   
Probably not because a hand-rolled file tree walker is going to do the 
same things that walkFileTree does. That said, there is one optimization 
that we can do on Windows to partly workaround the performance issues 
that are often reported on FAT32 and SMB.

> Also besides this question, i hope you don't think it too cheeky for
> me to post my function here for advice. Windows takes about 6 seconds
> find the files (in the explorer given a * regex) , java 49 seconds,
> This on a usb port. On a usb 2 port times become 3s windows and 21
> seconds java.
>   
That is a significant difference and probably explained by usage of 
isDirectory to check if each file is a directory. If I understand 
correctly, then the following code fragment is probably close to what 
you want:

    static List<Path> findMySource(Path start) {
        final List<Path> results = new ArrayList<Path>();
        final PathMatcher matcher =
            start.getFileSystem().getPathMatcher("glob:*.java");
        Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
            public FileVisitResult visitFile(Path file, 
BasicFileAttributes attrs) {
                if (matcher.matches(file.getName()))
                    results.add(file);
                return FileVisitResult.CONTINUE;
            }
        });
        return results;
    }

-Alan.