I must admit, I'm having a little bit of trouble.  My hmac result is
not coming back the same as the third-party vendor's hmac result.

When I am creating a MAC for a String, do I simply use
myString.getBytes() in order to feed it to this hmac routine?  I
assumed so, but I can't figure out why I'm getting the wrong results.

Also just to note, I am using the following routines to convert values
between byte arrays and hex strings. (My key is provided as a hex
string, and the mac hash needs to be communicated back as a hex string)

// Fast convert a byte array to a hex string
// with possible leading zero.
public static String toHexString ( byte[] b )
  {
  StringBuffer sb = new StringBuffer( 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();
  }

// 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;
  }

/**
* 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 );
     }
  }