Java 8 Stream with batch processing

Question

I have a large file that contains a list of items.

I would like to create a batch of items, make an HTTP request with this batch (all of the items are needed as par

Answer 1

I wrote a custom Spliterator for scenarios like this. It will fill lists of a given size from the input Stream. The advantage of this approach is that it will perform lazy processing, and it will work with other stream functions.

public static  Stream> batches(Stream stream, int batchSize) {
    return batchSize <= 0
        ? Stream.of(stream.collect(Collectors.toList()))
        : StreamSupport.stream(new BatchSpliterator<>(stream.spliterator(), batchSize), stream.isParallel());
}

private static class BatchSpliterator implements Spliterator> {

    private final Spliterator base;
    private final int batchSize;

    public BatchSpliterator(Spliterator base, int batchSize) {
        this.base = base;
        this.batchSize = batchSize;
    }

    @Override
    public boolean tryAdvance(Consumer> action) {
        final List batch = new ArrayList<>(batchSize);
        for (int i=0; i < batchSize && base.tryAdvance(batch::add); i++)
            ;
        if (batch.isEmpty())
            return false;
        action.accept(batch);
        return true;
    }

    @Override
    public Spliterator> trySplit() {
        if (base.estimateSize() <= batchSize)
            return null;
        final Spliterator splitBase = this.base.trySplit();
        return splitBase == null ? null
                : new BatchSpliterator<>(splitBase, batchSize);
    }

    @Override
    public long estimateSize() {
        final double baseSize = base.estimateSize();
        return baseSize == 0 ? 0
                : (long) Math.ceil(baseSize / (double) batchSize);
    }

    @Override
    public int characteristics() {
        return base.characteristics();
    }

}