Get a list of resources from classpath directory

Question

I am looking for a way to get a list of all resource names from a given classpath directory, something like a method List getResourceNames (String direct

Answer 1

I think you can leverage the [Zip File System Provider][1] to achieve this. When using FileSystems.newFileSystem it looks like you can treat the objects in that ZIP as a "regular" file.

In the linked documentation above:

Specify the configuration options for the zip file system in the java.util.Map object passed to the FileSystems.newFileSystem method. See the [Zip File System Properties][2] topic for information about the provider-specific configuration properties for the zip file system.

Once you have an instance of a zip file system, you can invoke the methods of the [java.nio.file.FileSystem][3] and [java.nio.file.Path][4] classes to perform operations such as copying, moving, and renaming files, as well as modifying file attributes.

The documentation for the jdk.zipfs module in [Java 11 states][5]:

The zip file system provider treats a zip or JAR file as a file system and provides the ability to manipulate the contents of the file. The zip file system provider can be created by [FileSystems.newFileSystem][6] if installed.

Here is a contrived example I did using your example resources. Note that a .zip is a .jar, but you could adapt your code to instead use classpath resources:

Setup

cd /tmp
mkdir -p x/y/z
touch x/y/z/{a,b,c}.html
echo 'hello world' > x/y/z/d
zip -r example.zip x

Java

import java.io.IOException;
import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.util.Collections;
import java.util.stream.Collectors;

public class MkobitZipRead {

  public static void main(String[] args) throws IOException {
    final URI uri = URI.create("jar:file:/tmp/example.zip");
    try (
        final FileSystem zipfs = FileSystems.newFileSystem(uri, Collections.emptyMap());
    ) {
      Files.walk(zipfs.getPath("/")).forEach(path -> System.out.println("Files in zip:" + path));
      System.out.println("-----");
      final String manifest = Files.readAllLines(
          zipfs.getPath("x", "y", "z").resolve("d")
      ).stream().collect(Collectors.joining(System.lineSeparator()));
      System.out.println(manifest);
    }
  }

}

Output

Files in zip:/
Files in zip:/x/
Files in zip:/x/y/
Files in zip:/x/y/z/
Files in zip:/x/y/z/c.html
Files in zip:/x/y/z/b.html
Files in zip:/x/y/z/a.html
Files in zip:/x/y/z/d
-----
hello world