groupingBy で chunk

grouping by のメモ

Map<String, Long> countmap = authors.stream().collect(Collectors.groupingBy(t->t.level, Collectors.counting()));
Map<String, List<Author>> mapAuthors = authors.stream().collect(Collectors.groupingBy(t->t.level, Collectors.mapping(u->u, Collectors.toList())));

Stream の grouping by は、chunk リストを作るの役立つ

AtomicInteger　を利用して、３個ずつに分けたリストのコレクションを生成

AtomicInteger counter = new AtomicInteger();
Collection<List<Author>> chunklist = authors.stream().collect(Collectors.groupingBy(t->counter.getAndIncrement() / 3 , Collectors.mapping(u->u, Collectors.toList()))).values();