question: static byte [ ] hexToBytes ( String hex ) { if ( hex == null ) { return EMPTY_BYTES ; } hex = hex . replaceAll ( "\\s+" , "" ) ; if ( hex . length ( ) == 0 ) { return EMPTY_BYTES ; } ByteArrayOutputStream baos = new ByteArrayOutputStream ( hex . length ( ) / 2 ) ; byte b ; for ( int i = 0 ; i < hex . length ( ) ; i ++ ) { int high = charToNibble ( hex . charAt ( i ) ) ; int low = 0 ; if ( i < hex . length ( ) - 1 ) { i ++ ; low = charToNibble ( hex . charAt ( i ) ) ; } b = ( byte ) ( high << 4 | low ) ; baos . write ( b ) ; } return baos . toByteArray ( ) ; }
target:  Utility method to convert byte array to a hex string. 