Convert a string representation of a hex dump to a

Question

I am looking for a way to convert a long string (from a dump), that represents hex values into a byte array.

I couldn't have phrased it better than the person that posted the same question here.

But to keep it original, I'll phrase it my own way: suppose I have a string "00A0BF" that I would like interpreted as the

byte[] {0x00,0xA0,0xBf}

what should I do?

I am a Java novice and ended up using BigInteger and watching out for leading hex zeros. But I think it is ugly and I am sure I am missing something simple.

Answer 1

You can now use BaseEncoding in guava to accomplish this.

BaseEncoding.base16().decode(string);

To reverse it use

BaseEncoding.base16().encode(bytes);

Answer 2

The BigInteger() Method from java.math is very Slow and not recommandable.

Integer.parseInt(HEXString, 16)

can cause problems with some characters without converting to Digit / Integer

a Well Working method:

Integer.decode("0xXX") .byteValue()

Function:

public static byte[] HexStringToByteArray(String s) {
    byte data[] = new byte[s.length()/2];
    for(int i=0;i < s.length();i+=2) {
        data[i/2] = (Integer.decode("0x"+s.charAt(i)+s.charAt(i+1))).byteValue();
    }
    return data;
}

Have Fun, Good Luck

Answer 3

I like the Character.digit solution, but here is how I solved it

public byte[] hex2ByteArray( String hexString ) {
    String hexVal = "0123456789ABCDEF";
    byte[] out = new byte[hexString.length() / 2];

    int n = hexString.length();

    for( int i = 0; i < n; i += 2 ) {
        //make a bit representation in an int of the hex value 
        int hn = hexVal.indexOf( hexString.charAt( i ) );
        int ln = hexVal.indexOf( hexString.charAt( i + 1 ) );

        //now just shift the high order nibble and add them together
        out[i/2] = (byte)( ( hn << 4 ) | ln );
    }

    return out;
}

Answer 4

My formal solution:

/**
 * Decodes a hexadecimally encoded binary string.
 * <p>
 * Note that this function does <em>NOT</em> convert a hexadecimal number to a
 * binary number.
 *
 * @param hex Hexadecimal representation of data.
 * @return The byte[] representation of the given data.
 * @throws NumberFormatException If the hexadecimal input string is of odd
 * length or invalid hexadecimal string.
 */
public static byte[] hex2bin(String hex) throws NumberFormatException {
    if (hex.length() % 2 > 0) {
        throw new NumberFormatException("Hexadecimal input string must have an even length.");
    }
    byte[] r = new byte[hex.length() / 2];
    for (int i = hex.length(); i > 0;) {
        r[i / 2 - 1] = (byte) (digit(hex.charAt(--i)) | (digit(hex.charAt(--i)) << 4));
    }
    return r;
}

private static int digit(char ch) {
    int r = Character.digit(ch, 16);
    if (r < 0) {
        throw new NumberFormatException("Invalid hexadecimal string: " + ch);
    }
    return r;
}

Is like the PHP hex2bin() Function but in Java style.

Example:

String data = new String(hex2bin("6578616d706c65206865782064617461"));
// data value: "example hex data"

Answer 5

One-liners:

import javax.xml.bind.DatatypeConverter;

public static String toHexString(byte[] array) {
    return DatatypeConverter.printHexBinary(array);
}

public static byte[] toByteArray(String s) {
    return DatatypeConverter.parseHexBinary(s);
}

Warnings:

• in Java 9 Jigsaw this is no longer part of the (default) java.se root set so it will result in a ClassNotFoundException unless you specify --add-modules java.se.ee (thanks to @eckes)
• Not available on Android (thanks to Fabian for noting that), but you can just take the source code if your system lacks javax.xml for some reason. Thanks to @Bert Regelink for extracting the source.

Answer 6

The Hex class in commons-codec should do that for you.

http://commons.apache.org/codec/

import org.apache.commons.codec.binary.Hex;
...
byte[] decoded = Hex.decodeHex("00A0BF");
// 0x00 0xA0 0xBF