flatMap

List list = Lists.newArrayList();

list.add(OptionDTO.builder().value(1).name("张三").build());

list.add(OptionDTO.builder().value(2).name("李四").build());

list.add(OptionDTO.builder().value(3).name("王五").build());

List> listList = Lists.newArrayList();

listList.add(list);

List flatList=listList.stream().flatMap(Collection::stream).collect(Collectors.toList());

System.out.println(JSON.toJSONString(flatList));

=========================

[{"name":"张三","value":1},{"name":"李四","value":2},{"name":"王五","value":3}]