Core Java

Playing with Java 8 – Lambdas, Paths and Files

I needed to read a whole bunch of files recently and instead of just grabbing my old that I and probably most developers have and then copy from project to project, I decided to have quick look at how else to do it…

Yes, I know there is Commons IO and Google IO, why would I even bother?  They probably do it better, but I wanted to check out the NIO jdk classes and play with lambdas as well…and to be honest, I think this actually ended up being a very neat bit of code.

So I had a specific use case:
I wanted to read all the source files from a whole directory tree, line by line.

What this code does, it uses Files.walk to recursively get all the paths from the starting point, it creates a stream, which I then filter to only files that end with the required extension. For each of those files, I use Files.lines to create a stream of Strings, one per line. I trim that, filter out the empty ones and add them to the return collection.

All very concise thanks to the new constructs.


import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.nio.charset.Charset;
import java.nio.file.FileVisitOption;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

 * RecursiveFileLineReader
 * Created by Brian on 2014-05-26.
public class RecursiveFileLineReader {

    private transient static final Log LOG = LogFactory.getLog(RecursiveFileLineReader.class);

     * Get all the non empty lines from all the files with the specific extension, recursively.
     * @param path      the path to start recursion
     * @param extension the file extension
     * @return list of lines
    public static List<String> readAllLineFromAllFilesRecursively(final String path, final String extension) {
        final List<String> lines = new ArrayList<>();
        try (final Stream<Path> pathStream = Files.walk(Paths.get(path), FileVisitOption.FOLLOW_LINKS)) {
                    .filter((p) -> !p.toFile().isDirectory() && p.toFile().getAbsolutePath().endsWith(extension))
                    .forEach(p -> fileLinesToList(p, lines));
        } catch (final IOException e) {
            LOG.error(e.getMessage(), e);
        return lines;

    private static void fileLinesToList(final Path file, final List<String> lines) {
        try (Stream<String> stream = Files.lines(file, Charset.defaultCharset())) {
                    .filter(s -> !s.isEmpty())
        } catch (final IOException e) {
            LOG.error(e.getMessage(), e);


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