java java8 List去重，按指定字段分组，按字段排序操作（持续更新）

//按指定字段去重（java8）
List<hysysLeftDataDTO> countLeftData = hysysLeftDataDTOList.stream().collect(Collectors.collectingAndThen(
	Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(hysysLeftDataDTO::getFirstLeftTitle))),ArrayList::new
));

//按指定字段分组（单字段java8）
Map<String, List<hysysLeftDataDTO>> groupBy = hysysLeftDataDTOList.stream().collect(Collectors.groupingBy(hysysLeftDataDTO::getFirstLeftTitle));
//按指定字段分组（多字段java8）
Map<String, List<LeftDataDTO>> groupBy = leftDataDTOList.stream().collect(
	Collectors.groupingBy(
		leftDataDTO -> leftDataDTO.getFileCode() +'/'+ leftDataDTO.getFileName() +'/'+ leftDataDTO.getDocumentName()

//单字段排序
firstGroupByCodeNameDoc.sort((a,b)->a.getArea().compareTo(b.getArea()));
//多字段排序（非Java8）
Collections.sort(firstGroupByCodeNameDoc, new Comparator<LeftDataDTO>() {
	@Override
	public int compare(LeftDataDTO o1, LeftDataDTO o2) {
		if(o2.getArea().compareTo(o1.getArea()) != 0){
			return o1.getArea().compareTo(o2.getArea());
		}
		else{
			return o1.getDevice().compareTo(o2.getDevice());
		}
	}
	});
));

//循环遍历分组后的值与取值
for (Map.Entry<String, List<hysysLeftDataDTO>> stringListEntry : groupBy.entrySet()) {
            //获取分组的value值
            List<hysysLeftDataDTO> groupByFirstLeftTitle = stringListEntry.getValue();
            CellRange firstTitle = sheet.getCellRange(LeftCount,1);
            firstTitle.setValue(stringListEntry.getKey());