FatJarLauncher.java

package com.ra4king.fatjar;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.util.Enumeration;
import java.util.Random;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

import javax.swing.JOptionPane;

public class FatJarLauncher {
    public static void main(String[] args) {
        JarFile jar;
        try {
            jar = new JarFile(new File(FatJarLauncher.class.getProtectionDomain().getCodeSource().getLocation().toURI()));
        }
        catch(Exception exc) {
            exc.printStackTrace();
            JOptionPane.showMessageDialog(null, "Error while opening up jar file");
            return;
        }

        File file = new File(System.getProperty("java.io.tmpdir").concat("/natives").concat(String.valueOf(new Random().nextInt())).concat("/"));

        if(!file.exists())
            file.mkdir();

        try {
            for(Enumeration<JarEntry> e = jar.entries(); e.hasMoreElements();) {
                JarEntry entry = e.nextElement();

                if(entry.getName().contains("/"))
                    continue;

                if(isNative(entry.getName())) {
                    try {
                        FileOutputStream fos = new FileOutputStream(new File(file,entry.getName()));

                        InputStream in = jar.getInputStream(entry);

                        byte[] data = new byte[1024];
                        int len;
                        while((len = in.read(data)) != -1)
                            fos.write(data,0,len);

                        in.close();
                        fos.close();
                    }
                    catch(Exception exc) {
                        exc.printStackTrace();
                        JOptionPane.showMessageDialog(null, "Error while extracting natives");
                        return;
                    }
                }
            }

            try {
                Process p = Runtime.getRuntime().exec("java -Djava.library.path=\"" + file.getAbsolutePath() + "\" -cp \"" + jar.getName() + "\" " + jar.getManifest().getMainAttributes().getValue("Launcher-Main-Class"));

                p.waitFor();
            }
            catch(Exception exc) {
                exc.printStackTrace();
                JOptionPane.showMessageDialog(null, "Error while launching application.");
            }
        }
        finally {
            deleteDir(file);
        }
    }

    private static boolean isNative(String path) {
        path = path.toLowerCase();

        String os = System.getProperty("os.name").toLowerCase();

        if(os.startsWith("win"))
            return path.endsWith(".dll");

        if(os.startsWith("linux"))
            return path.endsWith(".so");

        if(os.startsWith("mac") || os.startsWith("darwin"))
            return path.endsWith(".dylib") || path.endsWith(".jnilib");

        return false;
    }

    private static void deleteDir(File file) {
        for(File f : file.listFiles()) {
            if(f.isDirectory())
                deleteDir(f);

            f.delete();
        }

        file.delete();
    }
}