HexUtil.java

package org.caudexorigo.text;

public class HexUtil
{

	// table to convert a nibble to a hex char.
	static char[] hexChar = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

	/**
	 * Convert a hex string to a byte array. Permits upper or lower case hex.
	 * 
	 * @param s
	 *            String must have even number of characters. and be formed only of digits 0-9 A-F or a-f. No spaces, minus or plus signs.
	 * @return corresponding byte array.
	 */
	public static byte[] fromHexString(String s)
	{
		int stringLength = s.length();
		if ((stringLength & 0x1) != 0)
		{
			throw new IllegalArgumentException("fromHexString requires an even number of hex characters");
		}
		byte[] b = new byte[stringLength / 2];

		for (int i = 0, j = 0; i < stringLength; i += 2, j++)
		{
			int high = charToNibble(s.charAt(i));
			int low = charToNibble(s.charAt(i + 1));
			b[j] = (byte) ((high << 4) | low);
		}
		return b;
	}

	// Fast convert a byte array to a hex string
	// with possible leading zero.

	public static String toHexString(byte[] b)
	{
		StringBuilder sb = new StringBuilder(b.length * 2);
		for (int i = 0; i < b.length; i++)
		{
			// look up high nibble char
			sb.append(hexChar[(b[i] & 0xf0) >>> 4]);

			// look up low nibble char
			sb.append(hexChar[b[i] & 0x0f]);
		}
		return sb.toString();
	}

	/**
	 * convert a single char to corresponding nibble.
	 * 
	 * @param c
	 *            char to convert. must be 0-9 a-f A-F, no spaces, plus or minus signs.
	 * 
	 * @return corresponding integer
	 */
	private static int charToNibble(char c)
	{
		if ('0' <= c && c <= '9')
		{
			return c - '0';
		}
		else if ('a' <= c && c <= 'f')
		{
			return c - 'a' + 0xa;
		}
		else if ('A' <= c && c <= 'F')
		{
			return c - 'A' + 0xa;
		}
		else
		{
			throw new IllegalArgumentException("Invalid hex character: " + c);
		}
	}
}