HexString2byte.java

public static String getHexString(byte[] b) throws Exception {
  String result = "";
  for (int i=0; i < b.length; i++) {
    result += Integer.toString( ( b[i] & 0xff ) + 0x100, 16).substring( 1 );
  }
  return result;
}

public static byte[] getByteArray(String hexString) {
  return BigInteger(hexString,16).toByteArray(); 
}