java stream groupingby分组后排序重构val

java8 stream中使用分组排序 分组获取最大、最小值;

实体类中 list列表中分组排序

实体类

@Data
@Accessors(chain = true)
public class Users {
    private Integer age;
    private String name;
    private Integer sex;
}

分组后排序

 Map<String, List<Users>> sortUsers = objects.stream()
                .collect(Collectors.groupingBy(Users::getName, CommonUtils.toSortedList(
                        Comparator.comparing(Users::getAge)
                                .reversed())));
//收集器
public static <T> Collector<T, ?, List<T>> toSortedList(Comparator<? super T> c) {
        return Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(c)), ArrayList::new);
    }

分组后获取最大、最小实体

Map<String, Users> sortUsersMax = objects.stream()
                .collect(Collectors.groupingBy(Users::getName,                    CommonUtils.toSorted(Comparator.comparing(Users::getAge))));

//收集器 如果获取最小值  Collectors.maxBy(c) -》 Collectors.minBy(c)

public static <T> Collector<T, ?, T> toSorted(Comparator<? super T> c) {
        Collector<T, ?, T> usersObjectUsersCollector = Collectors.collectingAndThen(Collectors.maxBy(c), Optional::get);
        return usersObjectUsersCollector;
    }

重构分组key 以及value

//获取省市映射关系
        Map<String, List<String>> pCityDataMap = cityValues.stream()
                                                               .collect(Collectors.groupingBy(k ->
                                                                               Optional.ofNullable(pCodeName.get(k.getPCode()))
                                                                                       .orElse(Integer.toString(-1)),
                                                                       Collectors.mapping(CityDto::getName,
                                                                               Collectors.toList())));
        //获取市区映射关系
        Map<String, List<String>> cAreaDataMap = areaValues.stream()
                                                           .collect(Collectors.groupingBy(k -> Optional.ofNullable(cCodeName.get(k.getCCode()))
                                                                                                       .orElse(Integer.toString(-1)),
                                                                   Collectors.mapping(AreaDto::getName,
                                                                           Collectors.toList())));