final Optional<String> concatenatedNames = players.stream().map(player -> {
    final String[] namePart = player.getName().split(" ");
    if (namePart.length == 2) {
        return namePart[0] + " " + namePart[1].toUpperCase();
    } else {
        return player.getName();
    }
}).reduce((a, b) -> a + ", " + b);
out.println(concatenatedNames);

assertThat(concatenatedNames).isPresent().hasValue("Cristiano RONALDO, Ali DAEI, Lionel MESSI, Sunil CHHETRI");