Avoiding "null-check" in List processing using Optional of Java 8

Question

In Class Site, I have two utility methods.

The first one, parseStub, parses a Site into a Master if no errors occur; otherwise, it returns null. Using Optional:

public static Optional<Master> parseStub(Site site) {
    // do some parse work; return Optional.empty() if the parse fails.
}

The second method parseStubs is to parse a list of Site into a list of Master. It reuses parseStub, and has to handle the possibly empty Optional<Master>:

public static List<Master> parseStubs(List<Site> sites) {
    return sites.stream()
            .<Master>map(site -> Site.parseStub(site).orElse(null))
            .filter(Objects::nonNull)
            .collect(Collectors.toList());
}

Note that in the code above, I introduced null again.
How could I avoid null (and filter(Objects::nonNull)) using Optional consistently?

Java 9: flatMap(site -> Site.parseStub(site).stream()).collect(toList()) — Holger
– Holger, Commented Dec 9, 2015 at 9:41

Brian Goetz · Accepted Answer · 2015-12-09 04:31:04Z

7

Here's one way:

return sites.stream()
        .map(Site::parseStub)
        .filter(Optional::isPresent)
        .map(Optional::get)
        .collect(Collectors.toList());

answered Dec 9, 2015 at 4:31

Brian Goetz

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