About Lukas Eder

Lukas is a Java and SQL enthusiast developer. He created the Data Geekery GmbH. He is the creator of jOOQ, a comprehensive SQL library for Java, and he is blogging mostly about these three topics: Java, SQL and jOOQ.

Java 8 Friday Goodies: java.io finally rocks!

At Data Geekery, we love Java. And as we’re really into jOOQ’s fluent API and query DSL, we’re absolutely thrilled about what Java 8 will bring to our ecosystem. We have blogged a couple of times about some nice Java 8 goodies, and now we feel it’s time to start a new blog series, the…

Java 8 Friday

Every Friday, we’re showing you a couple of nice new tutorial-style Java 8 features, which take advantage of lambda expressions, extension methods, and other great stuff. You’ll find the source code on GitHub.

Java 8 Goodie: java.io with Lambdas

Interacting with the file system has been a bit of a pain in Java. CTMMC shows us an example of how to copy a file with Java. While some issues still remain, at least, we can now use lambdas and the new Streams API to traverse the file system and list files! Here is the FileFilterGoodies example that we’ve pushed to our GitHub repository:

public class FileFilterGoodies {

    public static void main(String args[]) {
        listRecursive(new File("."));

     * This method recursively lists all
     * .txt and .java files in a directory
    private static void listRecursive(File dir) {
        Arrays.stream(dir.listFiles((f, n) ->
                  ||  n.endsWith(".txt")
                  ||  n.endsWith(".java"))
              .forEach(unchecked((file) -> {
                          .substring(new File(".")

                  if (file.isDirectory()) {

     * This utility simply wraps a functional
     * interface that throws a checked exception
     * into a Java 8 Consumer
    private static <T> Consumer<T>
    unchecked(CheckedConsumer<T> consumer) {
        return t -> {
            try {
            catch (Exception e) {
                throw new RuntimeException(e);

    private interface CheckedConsumer<T> {
        void accept(T t) throws Exception;

The output of the above programme is:

\jOOQ's Java 8 Goodies.iml
\out\production\jOOQ's Java 8 Goodies
\out\production\jOOQ's Java 8 Goodies\org
\out\production\jOOQ's Java 8 Goodies\org\jooq
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8\goodies
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8\goodies\io
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8\goodies\io\FileFilterGoodies$CheckedConsumer.class
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8\goodies\io\FileFilterGoodies.class

Now, that’s really awesome, isn’t it? Let’s decompose the above listRecursive() method:

// With this method, we wrap the File[] array
// into a new Java 8 Stream, which has awesome
// new methods.

// The Java 1.2 File.listFiles() method luckily
// accepts a @FunctionalInterface, which can be
// instantiated using a lambda expression
// ...
// In this example, we'll just ignore the fact
// that listFiles can return null
              dir.listFiles((f, n) ->
          ||  n.endsWith(".txt")
          ||  n.endsWith(".java"))

// Each Stream (and also java.util.List) has this
// awesome forEach method, that accepts a Consumer

// Unfortunately, Java 8 Consumers don't allow
// throwing checked exceptions. So let's quickly
// wrap it (see details below) ...

// ... and pass another lambda expression to it,
// which prints the local path and recurses
                         (file) -> {
                  .substring(new File(".")

          if (file.isDirectory()) {

More goodies next week

Stay tuned for next week, when we show you how Java 8 improves using XML with jOOX

Related Whitepaper:

Bulletproof Java Code: A Practical Strategy for Developing Functional, Reliable, and Secure Java Code

Use Java? If you do, you know that Java software can be used to drive application logic of Web services or Web applications. Perhaps you use it for desktop applications? Or, embedded devices? Whatever your use of Java code, functional errors are the enemy!

To combat this enemy, your team might already perform functional testing. Even so, you're taking significant risks if you have not yet implemented a comprehensive team-wide quality management strategy. Such a strategy alleviates reliability, security, and performance problems to ensure that your code is free of functionality errors.Read this article to learn about this simple four-step strategy that is proven to make Java code more reliable, more secure, and easier to maintain.

Get it Now!  

One Response to "Java 8 Friday Goodies: java.io finally rocks!"

  1. selcuk says:

    I hope it does rock, But the code example you gave here is hard to read. I’m suspicious about lambdas.They can easily make the code get hard to understand.
    thank you

Leave a Reply

six + = 10

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.

Sign up for our Newsletter

20,709 insiders are already enjoying weekly updates and complimentary whitepapers! Join them now to gain exclusive access to the latest news in the Java world, as well as insights about Android, Scala, Groovy and other related technologies.

As an extra bonus, by joining you will get our brand new e-books, published by Java Code Geeks and their JCG partners for your reading pleasure! Enter your info and stay on top of things,

  • Fresh trends
  • Cases and examples
  • Research and insights
  • Two complimentary e-books