package replaceHeader;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;

public class replaceHeader {

    static String hexString = ""; // A hex string that you want to use as replacement for the first 512 bits. 512 bits in hex is 1024 characters
    static byte[] headerBits = hexStringToByteArray(hexString);
    static File fil;

    static String path = "/path/to/folder/containing/files"; // EDIT THIS!!

    public static void main(String[] args) throws IOException{



        File folder = new File(path);
        File[] listOfFiles = folder.listFiles();

        for(int i = 0; i < listOfFiles.length; i++){
            fil = new File(listOfFiles[i]+"");
            replaceBytes();
        }




    }
    public static byte[] hexStringToByteArray(String s) {
        int len = s.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                                 + Character.digit(s.charAt(i+1), 16));
        }
        return data;
    }
    public static void replaceBytes() throws IOException{
        RandomAccessFile raf = new RandomAccessFile(fil, "rw");
        try {
            raf.seek(0);
            raf.write(headerBits, 0, hexString.length()/2);
        } finally {
            raf.close();
        }
    }
}