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 FileUtils.java 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.

package net.briandupreez.blog.java8.io;

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

import java.io.IOException;
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;
import java.util.stream.Stream;

/**
 * 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)) {
            pathStream
                    .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())) {
            stream
                    .map(String::trim)
                    .filter(s -> !s.isEmpty())
                    .forEach(lines::add);
        } catch (final IOException e) {
            LOG.error(e.getMessage(), e);
        }
    }


}
Related Whitepaper:

Functional Programming in Java: Harnessing the Power of Java 8 Lambda Expressions

Get ready to program in a whole new way!

Functional Programming in Java will help you quickly get on top of the new, essential Java 8 language features and the functional style that will change and improve your code. This short, targeted book will help you make the paradigm shift from the old imperative way to a less error-prone, more elegant, and concise coding style that’s also a breeze to parallelize. You'll explore the syntax and semantics of lambda expressions, method and constructor references, and functional interfaces. You'll design and write applications better using the new standards in Java 8 and the JDK.

Get it Now!  

Leave a Reply


three × = 21



Java Code Geeks and all content copyright © 2010-2014, Exelixis Media Ltd | Terms of Use | Privacy Policy
All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners.
Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries.
Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation.
Do you want to know how to develop your skillset and become a ...
Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you two of our best selling eBooks for FREE!

Get ready to Rock!
You can download the complementary eBooks using the links below:
Close