A Java stream combinator that splits a stream into chunks of a fixed size. Last chunk in the stream might be smaller than the desired size. Ordering guarantees depend on underlying stream.

ChunkedStreams.java

public final class ChunkedStreams {
  private ChunkedStreams(){}
      @SuppressWarnings("SameParameterValue")
  public static <T> Stream<List<T>> chunks(Stream<T> sourceStream, int size) {
      var source = sourceStream.spliterator();
      return StreamSupport.stream(new Spliterator<>() {
          final List<T> buf = new ArrayList<>();

          @Override
          public boolean tryAdvance(Consumer<? super List<T>> action) {
              while (buf.size() < size) {
                  if (!source.tryAdvance(buf::add)) {
                      if (!buf.isEmpty()) {
                          action.accept(List.copyOf(buf));
                          buf.clear();
                          return true;
                      } else {
                          return false;
                      }
                  }
              }
              action.accept(List.copyOf(buf));
              buf.clear();
              return true;
          }

          @Override
          public Spliterator<List<T>> trySplit() {
              return null;
          }

          @Override
          public long estimateSize() {
              var sourceSize = source.estimateSize();
              return sourceSize / size + (sourceSize % size != 0 ? 1 : 0);
          }

          @Override
          public int characteristics() {
              return NONNULL | ORDERED;
          }
      }, false);
  }
}