Chaining Optionals in Java 8
Use a Stream:
Stream.of(find1(), find2(), find3())
.filter(Optional::isPresent)
.map(Optional::get)
.findFirst();
If you need to evaluate the find methods lazily, use supplier functions:
Stream.of(this::find1, this::find2, this::find3)
.map(Supplier::get)
.filter(Optional::isPresent)
.map(Optional::get)
.findFirst();
You could do it like this:
Optional<String> resultOpt = Optional.of(find1()
.orElseGet(() -> find2()
.orElseGet(() -> find3()
.orElseThrow(() -> new WhatEverException()))));
Though I'm not sure it improves readability IMO. Guava provides a way to chain Optionals:
import com.google.common.base.Optional;
Optional<String> resultOpt = s.find1().or(s.find2()).or(s.find3());
It could be another alternative for your problem but does not use the standard Optional class in the JDK.
If you want to keep the standard API, you could write a simple utility method:
static <T> Optional<T> or(Optional<T> first, Optional<T> second) {
return first.isPresent() ? first : second;
}
and then:
Optional<String> resultOpt = or(s.find1(), or(s.find2(), s.find3()));
If you have a lot of optionals to chains, maybe it's better to use the Stream approach as other mentionned already.
Inspired by Sauli's answer, it is possible to use the flatMap()
method.
Stream.of(this::find1, this::find2, this::find3)
.map(Supplier::get)
.flatMap(o -> o.map(Stream::of).orElseGet(Stream::empty))
.findFirst();
Converting an Optional into a Stream is cumbersome. Apparently, this is going to be fixed with JDK9. So this could be written as
Stream.of(this::find1, this::find2, this::find3)
.map(Supplier::get)
.flatMap(Optional::stream)
.findFirst();
Update after Java 9 was released
Although the original question was about Java 8, Optional::or
was introduced in Java 9. With it, the problem could be solved as follows
Optional<String> result = find1()
.or(this::find2)
.or(this::find3);