ToListCollector.java

    public static interface ReadOnlySpliterator {
        int characteristics();

        long estimateSize();

        long getExactSizeIfKnown();

        boolean hasCharacteristics(int characteristics);
    }

    public static <T> Collector<T, ?, List<T>> toList(ReadOnlySpliterator spliterator) {
        Supplier<List<T>> supplier;
        
        if (!spliterator.hasCharacteristics(Spliterator.CONCURRENT) &&
                spliterator.hasCharacteristics(Spliterator.SIZED)) {

            int size = (int) spliterator.getExactSizeIfKnown();
            supplier = () -> new ArrayList<>(size);
            
        } else {
            supplier = ArrayList::new;
        }
        
        return Collector.of(supplier, List::add,
                (left, right) -> { left.addAll(right); return left; });
    }