java集合分组排序

假设有这么个对象

@Data
@Accessors(chain = true)
public class OrderMapVo {
    private String launchDate;
    private String sexCode;
    private String categoryCode;
}

要实现基于launchDate有序分组，同时分组内的数据按sexCode，categoryCode排序，空值放最后。可以借助Collectors.collectingAndThen实现

List<OrderMapSeriesVo> list = new ArrayList<>();
// 填充数据...
// 排序
TreeMap<String, List<OrderMapVo>> dayMap = list.stream()
                .collect(Collectors.groupingBy(OrderMapVo::getLaunchDate, TreeMap::new,
                        Collectors.collectingAndThen(
                                Collectors.toList(),
                                sub->sub.stream().sorted(
                                        Comparator.comparing(OrderMapVo::getSexCode, Comparator.nullsLast(Comparator.naturalOrder()))
                                                .thenComparing(OrderMapVo::getCategoryCode, Comparator.nullsLast(Comparator.naturalOrder()))
                                ).collect(Collectors.toList())
                )));