java8 按两个属性分组，并返回扁平List； stream排序

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java8 按两个属性分组，并返回扁平List

    /**
     * 设置大区小区分组排序
     * @param dtoList
     */
    private List<PerformanceDto> getRegionGroupOrderList(List<PerformanceDto> dtoList) {
       return dtoList.stream()
                .collect(Collectors.groupingBy(PerformanceDto::getLargeRegion, Collectors.groupingBy(PerformanceDto::getSmallRegion)))
                .entrySet().stream()
                .flatMap(p -> p.getValue().entrySet().stream().flatMap(a -> a.getValue().stream()))
                .collect(Collectors.toList());
    }

排序：

List<Student> studentList1=studentList.stream().sorted().collect(Collectors.toList());//自然序列

List<Student> studentList2=studentList.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());//逆序

List<Student> studentList3=studentList.stream().sorted(Comparator.comparing(Student::getAge)).collect(Collectors.toList());//根据年龄自然顺序

List<Student> studentList4=studentList.stream().sorted(Comparator.comparing(Student::getAge).reversed()).collect(Collectors.toList());//根据年龄逆序