Esempio per estrazione file da jar:
codice:
import java.lang.*;
import java.io.*;
import java.net.*;

public class EstrazioneDaJar
{
    public static void main (String[] args)
    {
        try
        {
            URL url = EstrazioneDaJar.class.getResource ("path/immagine.jpg");

            InputStream is = url.openStream ();

            FileOutputStream fos = new FileOutputStream (new File ("estratto.jpg"));

            byte[] buff = new byte[512];
            int count;

            while ((count = is.read (buff)) > 0)
                fos.write (buff, 0, count);

            is.close ();
            fos.close ();
        }
        catch (Exception e)
        {
            e.printStackTrace ();
        }
    }
}