question: @ NonNull static String toHexString ( @ Nullable final byte [ ] src ) { if ( src == null ) { return "null" ; } final StringBuilder buffer = new StringBuilder ( ) ; buffer . append ( "[" ) ; boolean needComma = false ; for ( final byte srcByte : src ) { if ( needComma ) { buffer . append ( ", " ) ; } buffer . append ( String . format ( "%02x" , srcByte & 0xff ) ) ; needComma = true ; } buffer . append ( "]" ) ; return buffer . toString ( ) ; }
target:  Convert the byte array to the hex dumped string