Java byte array convert from hexadecimal digit String via ByteArrayOutputStream

import java.io.ByteArrayOutputStream;

public class Main {

   public static void main(String[] argv) {
      byte[] b = "demo2s.com".getBytes();
      String s = convert(b);/*  w w w.j  a  va 2  s.com*/
      System.out.println(s);

      b = convert(s);

      System.out.println(new String(b));
   }

   /**
    * Convert a String of hexadecimal digits into the corresponding byte array by
    * encoding each two hexadecimal digits as a byte.
    *
    * @param digits
    *          Hexadecimal digits representation
    *
    * @exception IllegalArgumentException
    *              if an invalid hexadecimal digit is found, or the input string
    *              contains an odd number of hexadecimal digits
    */
   public static byte[] convert(String digits) {

     ByteArrayOutputStream baos = new ByteArrayOutputStream();
     for (int i = 0; i < digits.length(); i += 2) {
       char c1 = digits.charAt(i);
       if ((i + 1) >= digits.length())
         throw new IllegalArgumentException("hexUtil.odd");
       char c2 = digits.charAt(i + 1);
       byte b = 0;
       if ((c1 >= '0') && (c1 <= '9'))
         b += ((c1 - '0') * 16);
       else if ((c1 >= 'a') && (c1 <= 'f'))
         b += ((c1 - 'a' + 10) * 16);
       else if ((c1 >= 'A') && (c1 <= 'F'))
         b += ((c1 - 'A' + 10) * 16);
       else
         throw new IllegalArgumentException("hexUtil.bad");
       if ((c2 >= '0') && (c2 <= '9'))
         b += (c2 - '0');
       else if ((c2 >= 'a') && (c2 <= 'f'))
         b += (c2 - 'a' + 10);
       else if ((c2 >= 'A') && (c2 <= 'F'))
         b += (c2 - 'A' + 10);
       else
         throw new IllegalArgumentException("hexUtil.bad");
       baos.write(b);
     }
     return (baos.toByteArray());

   }

   //Helper method for testing






   /**
    * Convert a byte array into a printable format containing a String of
    * hexadecimal digit characters (two per byte).
    *
    * @param bytes Byte array representation
    */
   public static String convert(byte bytes[]) {

      StringBuffer sb = new StringBuffer(bytes.length * 2);
      for (int i = 0; i < bytes.length; i++) {
         sb.append(convertDigit((int) (bytes[i] >> 4)));
         sb.append(convertDigit((int) (bytes[i] & 0x0f)));
      }
      return (sb.toString());

   }

   /**
    * Convert the specified value (0 .. 15) to the corresponding
    * hexadecimal digit.
    *
    * @param value Value to be converted
    */
   private static char convertDigit(int value) {

      value &= 0x0f;
      if (value >= 10)
         return ((char) (value - 10 + 'a'));
      else
         return ((char) (value + '0'));
   }

}