Created
October 30, 2015 10:11
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Lazy optional stream
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package optional; | |
import java.util.Optional; | |
import java.util.function.Supplier; | |
import java.util.stream.Stream; | |
public class StreamOfOptional { | |
public static void main(String[] args) { | |
System.out.println("--Before eager--"); | |
process(eager()); | |
System.out.println("--After eager--"); | |
System.out.println("--Before lazy--"); | |
process(lazy()); | |
System.out.println("--After lazy--"); | |
}; | |
private static void process(Stream<Optional<String>> stream) { | |
stream | |
.filter(Optional::isPresent).map(Optional::get) // if present, unpack | |
.peek(s -> System.out.println("processed: " + s)) // print, what is currently in the pipeline | |
.findFirst() | |
.ifPresent(System.out::println); | |
} | |
private static Stream<Optional<String>> lazy() { | |
// https://stackoverflow.com/a/28833677/3824515 | |
return Stream.<Supplier<Optional<String>>>of( | |
() -> firstOpt(), | |
() -> secondOpt() | |
) | |
.map(Supplier::get); | |
} | |
private static Stream<Optional<String>> eager() { | |
return Stream.of( | |
firstOpt(), | |
secondOpt() | |
); | |
} | |
private static Optional<String> firstOpt() { | |
return Optional.ofNullable("first") | |
.map(s-> { | |
System.out.println("Cheap mapping on '"+s+"' done."); | |
return s; | |
}); | |
} | |
private static Optional<String> secondOpt() { | |
return Optional.ofNullable("second") | |
.map(s-> { | |
System.out.println("Really expensive mapping on '"+s+"' done (e.g. DB access)!"); | |
return s; | |
}); | |
} | |
} |
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