[Java] Creating and extracting ZIP files

Code:
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.DirectoryIteratorException;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.HashSet;
import java.util.Set;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipOutputStream;

public class ZipCompression {

    private final static String SEP = System.getProperty("file.separator");

    public static void main(String[] args) throws FileNotFoundException,
            IOException {
        if (args.length != 2
                || (!args[0].equals("-x") && !args[0].equals("-a"))) {

            printUsage();

        } else {
            if (args[0].equals("-a")) {
                zip(args[1]);
            } else {
                unzip(args[1]);
            }
        }
    }

    /**
     * Creates a zip archive with inFiles as entries.
     *
     * @param inFiles
     *            files that shall be put to the archive
     * @param outFile
     *            zip archive that shall be created
     * @throws FileNotFoundException
     * @throws IOException
     */
    public static void zip(Set<Path> inFiles, Path outFile)
            throws FileNotFoundException, IOException {
        System.out.println("creating zip file " + outFile);
        try (ZipOutputStream zout = new ZipOutputStream(new FileOutputStream(
                outFile.toString())) {
            zip(inFiles, "", zout);
        }
    }

    /**
     * Extracts all files in zipFile to the destination directory.
     *
     * @param zipFile
     *            archive to extract
     * @param destinationDir
     *            directory, where the files shall be written to
     * @throws FileNotFoundException
     * @throws IOException
     */
    public static void unzip(Path zipFile, Path destinationDir)
            throws FileNotFoundException, IOException {
        System.out.println("extracting zip file " + zipFile);
        try (ZipInputStream zin = new ZipInputStream(new FileInputStream(
                zipFile.toString()))) {

            ZipEntry entry;
            while ((entry = zin.getNextEntry()) != null) {
                extractEntry(destinationDir, zin, entry);
            }
        }
    }

    /**
     * Creates a zip archive for all files in the given directory. The name of
     * the archive will be the directory name with the ending '.zip' and is
     * created in the parent directory.
     *
     * @param directoryName
     *            directory that shall be zipped
     * @throws FileNotFoundException
     * @throws IOException
     */
    public static void zip(String directoryName) throws FileNotFoundException,
            IOException {
        Path dir = Paths.get(directoryName);
        Set<Path> inFiles = getDirectoryFiles(dir);
        Path outFile = Paths.get(dir.toString() + ".zip");
        zip(inFiles, outFile);
    }

    private static void zip(Set<Path> inFiles, String base, ZipOutputStream zout)
            throws IOException, FileNotFoundException {
        for (Path file : inFiles) {
            if (Files.isDirectory(file)) {
                String filename = base + file.getFileName().toString();
                zip(getDirectoryFiles(file), filename + SEP, zout);
            } else {
                writeZipEntry(zout, file, base);
            }
        }
    }

    /**
     * Extracts all files of a given zip archive to the parent folder of the
     * archive.
     *
     * @param zipfileName
     *            archive to be extracted
     * @throws FileNotFoundException
     * @throws IOException
     */
    public static void unzip(String zipfileName) throws FileNotFoundException,
            IOException {
        Path zipFile = Paths.get(zipfileName);
        Path destinationDir = zipFile.getParent();
        unzip(zipFile, destinationDir);
    }

    private static void printUsage() {
        System.out.println("usage:");
        System.out.println("\tjava ZipCompression -x <zipfile>");
        System.out.println("\tjava ZipCompression -a <directory>");
    }

    private static Set<Path> getDirectoryFiles(Path dir) {
        Set<Path> dirFiles = new HashSet<>();
        try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir)) {
            for (Path file : stream) {
                dirFiles.add(file);
            }
        } catch (IOException | DirectoryIteratorException e) {
            e.printStackTrace();
        }
        return dirFiles;
    }

    private static void writeZipEntry(ZipOutputStream out, Path inFile,
            String base) throws IOException, FileNotFoundException {
        System.out.println("write zip entry " + inFile);
        try (FileInputStream in = new FileInputStream(inFile.toString())) {
            out.putNextEntry(new ZipEntry(base
                    + inFile.getFileName().toString()));
            byte[] buf = new byte[1024];
            int len;

            while ((len = in.read(buf)) != -1) {
                out.write(buf, 0, len);
            }
            out.closeEntry();
        }
    }

    private static void extractEntry(Path destinationDir, ZipInputStream zin,
            ZipEntry entry) throws IOException, FileNotFoundException {

        Path currentFile = Paths
                .get(destinationDir.toString(), entry.getName());
        System.out.println("extracting file " + currentFile);
        Files.createDirectories(currentFile.getParent());

        try (FileOutputStream out = new FileOutputStream(currentFile.toString())) {
            byte[] buf = new byte[1024];
            int len;
            while ((len = zin.read(buf)) != -1) {
                out.write(buf, 0, len);
            }
        }
        zin.closeEntry();
    }

}