use Java to convert ANY file to hex and back again

Question

I have some files i would like to convert to hex, alter, and then reverse again, but i have a problem trying to do jars, zips, and rars. It seems to only work on files containing normally readable text. I have looked all around but cant find anything that would allow jars or bats to do this correctly. Does anyone have an answer that does both? converts to hex then back again, not just to hex?

Answer 1

You can convert any file to hex. It's just a matter of obtaining a byte stream, and mapping every byte to two hexadecimal numbers.

Here's a utility class that lets you convert from a binary stream to a hex stream and back:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.Writer;

public class Hex {
    public static void binaryToHex(InputStream is, OutputStream os) {
        Writer writer = new BufferedWriter(new OutputStreamWriter(os));

        try {
            int value;

            while ((value = is.read()) != -1) {
                writer.write(String.format("%02X", value));
            }

            writer.flush();
        } catch (IOException e) {
            System.err.println("An error occurred");
        }
    }

    public static void hexToBinary(InputStream is, OutputStream os) {
        Reader reader = new BufferedReader(new InputStreamReader(is));

        try {
            char buffer[] = new char[2];

            while (reader.read(buffer) != -1) {
                os.write((Character.digit(buffer[0], 16) << 4)
                        + Character.digit(buffer[1], 16));
            }
        } catch (IOException e) {
            System.err.println("An error occurred");
        }
    }
}

Partly inspired by this sample from Mykong and this answer.

Answer 2

Don't use a Reader to read String / char / char[], use an InputStream to read byte / byte[].