Java 8 optionalMap Example

public interface OptionalMapper<T, R> {
    Optional<R> optionalMap(T t);
}

public class OptionalMapOp<T, R> implements IntermediateOp<T, R> {
    public final OptionalMapper<? super T, ? extends R> mapper;

    public OptionalMapOp(OptionalMapper<? super T, ? extends R> mapper) {
        this.mapper = Objects.requireNonNull(mapper);
    }

    @Override
    public int getOpFlags() {
        return StreamOpFlags.NOT_SORTED | StreamOpFlags.NOT_DISTINCT;
    }

    @Override
    public Iterator<R> wrapIterator(int flags, final Iterator<T> source) {
        return iterator(source, mapper);
    }

    @Override
    public Sink<T> wrapSink(int flags, Sink sink) {
        return new Sink.ChainedValue<T>(sink) {
            @Override
            public void accept(T t) {
                for (R r : Optionals.toIterable(mapper.optionalMap(t))) {
                    downstream.accept(r);
                }
            }
        };
    }

    public static<T, R> Iterator<R> iterator(final Iterator<T> source, final OptionalMapper<? super T, ? extends R> mapper) {
        Objects.requireNonNull(source);
        Objects.requireNonNull(mapper);

        return new OptionalMapIterator(source, mapper);
    }

    static class OptionalMapIterator<T, R> implements Iterator<R> {
        final Iterator<T> source;
        final OptionalMapper<? super T, ? extends R> mapper;

        boolean haveNext = false;
        Optional<? extends R> nextValue = Optional.<R>empty();

        OptionalMapIterator(final Iterator<T> source, final OptionalMapper<? super T, ? extends R> mapper) {
            this.source = source;
            this.mapper = mapper;
        }

        public void tryToGetNext() {
            if (!haveNext) {
                while (source.hasNext()) {
                    final T sourceNext = source.next();
                    nextValue = mapper.optionalMap(sourceNext);

                    if (nextValue.isPresent()) {
                        haveNext = true;
                        return;
                    }
                }
            }
        }

        @Override
        public boolean hasNext() {
            tryToGetNext();
            return haveNext;
        }

        @Override
        public R next() {
            tryToGetNext();

            if (haveNext) {
                final Optional<? extends R> result = nextValue;
                haveNext = false;
                nextValue = Optional.<R>empty();
                return result.get();
            } else {
                throw new NoSuchElementException();
            }
        }
    }
}

public class MoreStreams {
    // This is a quick and dirty example that works.
    // The cast and the generic types would have to be fixed for a non-throwaway implementation.
    public static <T, R> Stream<R> optionalMap(Stream<T> stream, OptionalMapper<? super T, R> mapper) {
        final ValuePipeline vp = (ValuePipeline) stream;
        final OptionalMapOp mapOp = new OptionalMapOp<>(mapper);
        return chainValue(vp, mapOp);
    }

    protected static <E_IN, E_OUT> Stream<E_OUT> chainValue(AbstractPipeline<E_IN, E_OUT> pipeline, IntermediateOp<E_OUT, E_OUT> op) {
        return new ValuePipeline<>(pipeline, op);
    }
}

public class ZipCodeTest {
    public static class Address {
        public final Optional<String> zipOption;
        public Address(Optional<String> zipOption) { this.zipOption = zipOption; }
    }
    public static class Person {
        public final Optional<Address> addressOption;
        public Person(Optional<Address> addressOption) { this.addressOption = addressOption; }
    }

    public static void main(String[] args) {
        List<Person> people = new ArrayList<Person>();
        people.add(new Person(Optional.<Address>empty()));
        people.add(new Person(new Optional(new Address(Optional.<String>empty()))));
        people.add(new Person(new Optional(new Address(new Optional("12345")))));
        people.add(new Person(new Optional(new Address(Optional.<String>empty()))));
        people.add(new Person(new Optional(new Address(new Optional("45678")))));
        people.add(new Person(new Optional(new Address(new Optional("98765")))));
        people.add(new Person(Optional.<Address>empty()));

        Stream<Person> s = people.stream();
        ValuePipeline vp = (ValuePipeline) s;

        // --------------------------------------------------------
        // Regular map example: JDK8 supports this...

        final List<Optional<Address>> optAddresses = new ArrayList<Optional<Address>>();
        // Using static function syntax to match later examples:
        MoreStreams.map(people.stream(), (p) -> p.addressOption).into(optAddresses);
        // Nicer Syntax is built into JDK:
        people.stream().map((p) -> p.addressOption).into(optAddresses);

        // --------------------------------------------------------
        // optionalMap(flatMap) example: JDK8 purposefully omits...

        final List<Address> addresses = new ArrayList<Address>();
        optionalMap(people.stream(), (p) -> p.addressOption).into(addresses);
        // If JDK8 had this built-in, the nicer syntax would be :
        //people.stream().optionalMap((p) -> p.addressOption).into(addresses);

        final List<String> zips = new ArrayList<String>();
        optionalMap(optionalMap(people.stream(), (p) -> p.addressOption), (a) -> a.zipOption).into(zips);
        // If JDK8 had this built-in, the nicer syntax would be :
        //people.stream().optionalMap((p) -> p.addressOption).optionalMap((a) -> a.zipOption).into(zips);
    }
}