question: public static byte [ ] hexStringToBytes ( String hexString ) { if ( hexString == null || hexString . equals ( "" ) ) { return null ; } hexString = hexString . toUpperCase ( ) ; int length = hexString . length ( ) / 2 ; char [ ] hexChars = hexString . toCharArray ( ) ; byte [ ] d = new byte [ length ] ; for ( int i = 0 ; i < length ; i ++ ) { int pos = i * 2 ; d [ i ] = ( byte ) ( charToByte ( hexChars [ pos ] ) << 4 | charToByte ( hexChars [ pos + 1 ] ) ) ; } return d ; }
target:  Convert hex string to byte[]  