Copy.java

import static java.nio.file.StandardCopyOption.REPLACE_EXISTING;

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.ProviderMismatchException;
import java.util.Collections;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
import java.util.stream.Stream;

/**
 * Recursive copy of directory from a folder on the file system or inside a jar to another folder.
 */
public class Copy {
    public static void main(String[] args) throws MalformedURLException {
        if (args == null || args.length < 2) {
            System.out.println("Usage: CopyDir <dir_from> <dir_to>, dir_from may start with file: or jar:file:");
            return;
        }
        String from = args[0];
        if (!from.startsWith("file:") || !from.startsWith("jar:")) {
            from = "file:" + from;
        }
        cp(new URL(from), Paths.get(args[1]));
    }

    @FunctionalInterface
    interface TriFunction<A, B, C, R> {
        R apply(A a, B b, C c);
    }

    /**
     * Copy a file or a directory recursively from the file system or within a jar file.
     *
     * @param fromUrl URL to a directory or file to copy
     * @param toPath  where copy the target to
     * @return true if operation successful
     */
    public static boolean cp(URL fromUrl, Path toPath) {
        if (fromUrl == null) {
            return false;
        }
        try {
            final Path from;
            TriFunction<Path, Path, Path, Path> getDest;
            URI fromUri = fromUrl.toURI();
            switch (fromUrl.getProtocol()) {
                case "file":
                    Path path = Paths.get(fromUri);
                    if (!Files.exists(path)) {
                        return false;
                    }
                    from = path.toRealPath();
                    getDest = (source, toDir, fromDir) -> toDir.resolve(fromDir.relativize(source));
                    break;

                case "jar":
                    final FileSystem fileSystem = FileSystems.newFileSystem(fromUri, Collections.emptyMap());
                    final String wholePath = fromUri.toString();
                    final String jarFile = fileSystem.toString();
                    if (!Files.exists(Paths.get(jarFile))) {
                        return false;
                    }
                    String jarName = Paths.get(fileSystem.toString()).getFileName().toString();
                    String pathInJar = wholePath.substring(wholePath.indexOf(jarName + "!") + jarName.length() + 1 /* taking ! into account */);
                    JarFile jar = new JarFile(jarFile);
                    JarEntry entry = jar.getJarEntry(pathInJar.startsWith("/") ? pathInJar.substring(1) : pathInJar);
                    if (entry == null) {
                        return false;
                    }
                    from = fileSystem.getPath(pathInJar);
                    getDest = (source, toDir, fromDir) -> toDir.resolve(fromDir.relativize(fileSystem.getPath(source.toString())).toString());

                    break;
                default:
                    System.out.printf("Unknown file system - %s%n", fromUrl.getProtocol());
                    return false;

            }
            // mkdir -p
            if (!Files.exists(toPath)) {
                Files.createDirectories(toPath);
            }
            Path to = toPath.toRealPath();

            System.out.printf("Copying %s to %s%n", fromUrl, to);
            try (Stream<Path> stream = Files.walk(from)) {
                stream.forEach(source -> copy(source, getDest.apply(source, to, from)));
            }
        } catch (IOException | URISyntaxException | ProviderMismatchException e) {
            System.out.println(e.getMessage());
            return false;
        }

        return true;
    }

    private static void copy(Path source, Path dest) {
        try {
            Files.copy(source, dest, REPLACE_EXISTING);
        } catch (IOException e) {
            throw new RuntimeException("Couldn't copy", e);
        }
    }

}