How to return Optional String using Java 8 streams

Question

This code should return the Optional String when given siteUrl contains key from the predefined list of pairs (or Optional.empty() otherwise).

Is there a better way than using new Pair(null, null) here? Or maybe change the whole expression?

static Optional<String> get(String siteUrl) {
    return Optional.ofNullable(URL_TO_ENVIRONMENT
            .stream()
            .filter(p -> siteUrl.contains(p.getKey()))
            .findFirst().orElse(new Pair(null, null)).getValue());
}

private static final List<Pair> URL_TO_ENVIRONMENT = buildList();

private static List<Pair> buildList() {
    return Arrays.asList(
            new Pair("aaa.mysite.com", "aaa_something"),
            new Pair("bbb.mysite.com", "bbb_something"),
            new Pair("ccc.mysite.com", "ccc_comething"));
}

Misha · Accepted Answer · 2015-05-30 17:44:56Z

5

return URL_TO_ENVIRONMENT.stream()
    .filter(p->siteUrl.contains(p.getKey()))
    .map(Pair::getvalue)
    .findFirst();

Do you specifically need the first match? if you just want any match, use findAny instead of findFirst.

answered May 30, 2015 at 17:44

Misha

28.3k7 gold badges66 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Alex Over a year ago

wow, this was fast. I actually just need "any match". thank you, Misha!

Tagir Valeev Over a year ago

I'd prefer URL_TO_ENVIRONMENT.stream().filter(p->siteUrl.contains(p.getKey())).findAny().map(Pair::getvalue);. This way mapping is done outside of the pipeline keeping the pipeline shorter (less stack depth, more chances for inlining, etc.).

Misha Over a year ago

@TagirValeev In my observation, stream-like operations on Optional (map, filter, flatMap) tend to throw people off. So I have a (very) slight preference to avoid them.

Holger Over a year ago

@Tagir Valeev: the total stack depth doesn’t matter as the hotspot still spans the same deep-most stack frames.

Tagir Valeev Over a year ago

@Holger: sometimes it does matter as it can hit the MaxInlineLevel limit, so you will have something not inlined which would be inlined otherwise. Will try to make some sample benchmark later...

|

Collectives™ on Stack Overflow

How to return Optional String using Java 8 streams

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related