Java Compress multiple files in to 1 file (and reduce file size by up to 70%)

Code
import java.io.DataOutputStream;

import java.io.File;

import java.io.FileOutputStream;

import java.io.IOException;

import java.nio.file.Files;

import java.nio.file.Path;

import java.nio.file.Paths;

import java.util.zip.GZIPOutputStream;

import javax.swing.filechooser.FileSystemView;



public class PackGZip {

    

    private static final File packDir, fileCache;

    

    static {

        packDir = new File(FileSystemView.getFileSystemView().getHomeDirectory(), "HF"); //this is the directory of the files it will compress

        fileCache = new File(packDir, "howbow.dat"); //this is the file it will compress to

    }



    public static void compressContents() {

        if(!packDir.exists()) {

            System.out.println("Packing directory does not exist!");

            return;

        }

        File[] datFiles = packDir.listFiles(f -> {

            //write your own custom file filter if you'd like

            return f.isFile();

        });

        try (GZIPOutputStream gzos = new GZIPOutputStream(new FileOutputStream(fileCache)); DataOutputStream dataFile = new DataOutputStream(gzos)) {

            dataFile.writeInt(datFiles.length);

            System.out.println("Appending " + datFiles.length + " entries to config");

            for (File f : datFiles) {

                int length = (int) f.length();

                dataFile.writeInt(length);

                String name = f.getName();

                dataFile.writeUTF(name);

                System.out.println(String.format("Appending to config bytes=%d name=%s", length, name));

                byte[] data = readFile(f);

                dataFile.write(data);

            }

        } catch (IOException e) {

            e.printStackTrace();

        }

    }



    private static byte[] readFile(File file) {

        try {

            Path path = Paths.get(file.getAbsolutePath());

            byte[] data = Files.readAllBytes(path);

            return data;

        } catch (IOException e) {

            e.printStackTrace();

            return null;

        }

    }



    public static void main(String[] args) {

        compressContents();

    }

}