public void append(final String str){
  if ((str != null) && (str.length() > 0)) {
    if (first) {
      first=false;
    }
 else {
      buffer.append(separator);
    }
    buffer.append(str);
  }
}

public void append ( final String str ) { if ( ( str != null ) && ( str . length ( ) > 0 ) ) { if ( first ) { first = false ; } else { buffer . append ( separator ) ; } buffer . append ( str ) ; } }
append a string , separate by space if not empty .
