A type following the Optional API that computes its value once and only after a "terminal operation" (like Stream).

LazyOptional.java

import java.util.Objects;
import java.util.Optional;
import java.util.Spliterator;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

public final class LazyOptional<T> {

    private final Supplier<Optional<T>> optionalSupplier;
    private final boolean suppressExceptions;
    private volatile Optional<T> optional;
    private volatile ReentrantLock lock = new ReentrantLock();

    private LazyOptional(Supplier<Optional<T>> optionalSupplier, boolean emptyOnException) {
        this.optionalSupplier = Objects.requireNonNull(optionalSupplier);
        this.suppressExceptions = emptyOnException;
    }

    private static final LazyOptional<?> EMPTY = new LazyOptional<>(Optional::empty, false);
    
    @SuppressWarnings("unchecked")
    public static <T> LazyOptional<T> empty() {
        return (LazyOptional<T>) EMPTY;
    }

    public static <T> LazyOptional<T> ofNullable(Supplier<? extends T> valueSupplier) {
        Objects.requireNonNull(valueSupplier);
        return new LazyOptional<>(() -> Optional.ofNullable(valueSupplier.get()), false);
    }

    public static <T> LazyOptional<T> fromOptional(Supplier<Optional<T>> optionalSupplier) {
        Objects.requireNonNull(optionalSupplier);
        return new LazyOptional<>(optionalSupplier, false);
    }

    public static <T> LazyOptional<T> fromOptional(Optional<T> optional) {
        Objects.requireNonNull(optional);
        return optional.isEmpty() 
                ? empty() 
                : new LazyOptional<>(() -> optional, false);
    }

    private Optional<T> maybeComputeOptional() {
        ReentrantLock _lock = lock;
        if (_lock != null) {
            _lock.lock();
            try {
                if (lock != null) {
                    optional = optionalSupplier.get();
                }
            } catch (Throwable t) {
                optional = Optional.empty();
                if (!suppressExceptions) throw t;
            } finally {
                lock = null;
                _lock.unlock();
            }
        }
        return optional;
    }

    // Terminal Operations
    public Optional<T> toOptional() {
        if (lock == null) return optional;
        else return maybeComputeOptional();
    }
    
    public T get() {
        return toOptional().get();
    }
    
    public boolean isPresent() {
        return toOptional().isPresent();
    }
    
    public boolean isEmpty() {
        return toOptional().isEmpty();
    }
    
    public void ifPresent(Consumer<? super T> action) {
        toOptional().ifPresent(action);
    }
    
    public void ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction) {
        toOptional().ifPresentOrElse(action, emptyAction);
    }
    
    public T orElse(T other) {
        return toOptional().orElse(other);
    }
    
    public T orElseGet(Supplier<? extends T> supplier) {
        return toOptional().orElseGet(supplier);
    }
    
    public T orElseThrow() {
        return toOptional().orElseThrow();
    }

    public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
        return toOptional().orElseThrow(exceptionSupplier);
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (!getClass().isInstance(obj)) return false;
        var other = getClass().cast(obj);

        return toOptional().equals(other.toOptional());
    }

    @Override
    public int hashCode() {
        return toOptional().hashCode();
    }

    // Non-terminal Operations
    public LazyOptional<T> emptyOnException() {
        return new LazyOptional<>(() -> toOptional(), true);
    }
    
    public LazyOptional<T> filter(Predicate<? super T> predicate) {
        Objects.requireNonNull(predicate);
        return new LazyOptional<>(() -> toOptional().filter(predicate), suppressExceptions);
    }

    public <U> LazyOptional<U> map(Function<? super T, ? extends U> mapper) {
        Objects.requireNonNull(mapper);
        return new LazyOptional<>(() -> toOptional().map(mapper), suppressExceptions);
    }

    public <U> LazyOptional<U> flatMap(Function<? super T, ? extends Optional<? extends U>> mapper) {
        Objects.requireNonNull(mapper);
        return new LazyOptional<>(() -> toOptional().flatMap(mapper), suppressExceptions);
    }

    public <U> LazyOptional<U> flatMapLazy(Function<? super T, ? extends LazyOptional<? extends U>> mapper) {
        Objects.requireNonNull(mapper);
        return new LazyOptional<>(() -> toOptional().flatMap(mapper.andThen(LazyOptional::toOptional)), suppressExceptions);
    }

    public LazyOptional<T> or(Supplier<? extends Optional<? extends T>> supplier) {
        Objects.requireNonNull(supplier);
        return new LazyOptional<>(() -> toOptional().or(supplier), suppressExceptions);
    }

    public Stream<T> stream() {
        return StreamSupport.stream(new LazyOptionalSpliterator(), false);
    }

    private final class LazyOptionalSpliterator implements Spliterator<T> {
        
        private static final int CHARACTERISTICS = IMMUTABLE | ORDERED | SIZED | SUBSIZED;
        
        @Override
        public int characteristics() {
            return CHARACTERISTICS;
        }

        @Override
        public long estimateSize() {
            return 1;
        }
        
        @Override
        public Spliterator<T> trySplit() {
            return null;
        }

        private boolean done = false;
        
        @Override
        public boolean tryAdvance(Consumer<? super T> action) {
            if (!done) {
                done = true;
                if (isPresent()) {
                    action.accept(get());
                    return true;
                }
            }
            return false;
        }
    }
}