How do you list all files in the Resources folder (java/scala)

Question

I am writing a function which needs to access a folder in the resources, and loop through all filenames, and if those match the criteria, those files are loaded.

new File(getClass.getResource("/images/sprites").getPath).listFiles()

returns a null pointer exception, where the directory tree follows Resources -> images -> sprites ->

Please can somebody point me in the right direction?

Answer 1

A zip file system using jar:file: URIs would be something like this:

    URI uri = MainApp.class.getResource("/images/sprites").toURI();
    Map<String, String> env = new HashMap<>();
    try (FileSystem zipfs = FileSystems.newFileSystem(uri, env)) {
        //Path path = zipfs.getPath("/images/icons16");
        for (Path path : zipfs.getRootDirectories()) {
            Files.list(path.resolve("/images/sprites"))
                    .forEach(p -> System.out.println("* " + p));
        }
    }

Here I show getRootDirectories to possibly iterate over all resources.

Using the Files.copy one may copy them etcetera.

---

After comment of @MrPowerGamerBR:

The solution above deals with a jar . A more general solution, not exposing the jar character, is:

    URI uri = MAinApp.class.getResource("/images/sprites"").toURI();
    Path dirPath = Paths.get(uri);
    Files.list(dirPath)
         .forEach(p -> System.out.println("* " + p));

(In fact one might even read lines from the directory itself, but this is the correct abstraction, using Path .)

Answer 2

Joop Eggen's answer is awesome, however it can only do one of two things:

• Read the resources content when running from a IDE
• Read the resources content when running the JAR via the command line

So here's a example (Kotlin, but it should be easy to migrate it to Java) that allows you to have both: Reading the resources content when running from a IDE or via the command line!

    val uri = MainApp::class.java.getResource("/locales/").toURI()
    val dirPath = try {
        Paths.get(uri)
    } catch (e: FileSystemNotFoundException) {
        // If this is thrown, then it means that we are running the JAR directly (example: not from an IDE)
        val env = mutableMapOf<String, String>()
        FileSystems.newFileSystem(uri, env).getPath("/locales/")
    }

    Files.list(dirPath).forEach {
        println(it.fileName)
        if (it.fileName.toString().endsWith("txt")) {
            println("Result:")
            println(Files.readString(it))
        }
    }