List all files from a directory recursively with Java

Assuming this is actual production code you'll be writing, then I suggest using the solution to this sort of thing that's already been solved - Apache Commons IO, specifically FileUtils.listFiles(). It handles nested directories, filters (based on name, modification time, etc).

For example, for your regex:

Collection files = FileUtils.listFiles(
  dir, 
  new RegexFileFilter("^(.*?)"), 
  DirectoryFileFilter.DIRECTORY
);

This will recursively search for files matching the ^(.*?) regex, returning the results as a collection.

It's worth noting that this will be no faster than rolling your own code, it's doing the same thing - trawling a filesystem in Java is just slow. The difference is, the Apache Commons version will have no bugs in it.

This is a very simple recursive method to get all files from a given root.

It uses the Java 7 NIO Path class.

private List<String> getFileNames(List<String> fileNames, Path dir) {
    try(DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
        for (Path path : stream) {
            if(path.toFile().isDirectory()) {
                getFileNames(fileNames, path);
            } else {
                fileNames.add(path.toAbsolutePath().toString());
                System.out.println(path.getFileName());
            }
        }
    } catch(IOException e) {
        e.printStackTrace();
    }
    return fileNames;
} 

In Java 8, it's a 1-liner via Files.find() with an arbitrarily large depth (eg 999) and BasicFileAttributes of isRegularFile()

public static printFnames(String sDir) {
    Files.find(Paths.get(sDir), 999, (p, bfa) -> bfa.isRegularFile()).forEach(System.out::println);
}

To add more filtering, enhance the lambda, for example all jpg files modified in the last 24 hours:

(p, bfa) -> bfa.isRegularFile()
  && p.getFileName().toString().matches(".*\\.jpg")
  && bfa.lastModifiedTime().toMillis() > System.currentMillis() - 86400000