java对年月分组 [201901,201902,201904,201906]->[[201901,201902],[201904],[201906]]

在这里插入代码片

    /**
     * 对list数组分组  [201901,201902,201906,201908] ->[201901,201902], [201906], [201908]
     * @return
     */
    public static Map<Integer,List<String>> getGroups(List<String> list){
        //月份补全 201902-201905 ->[201902,201903,201904,201905]
        List<String> middleDateList = DateUtil.getMiddleDateList(list.get(0), list.get(list.size() - 1));
        System.out.println(middleDateList);
        //差集
        List<String> reduce1 = middleDateList.stream().filter(item -> !list.contains(item)).collect(toList());
        System.out.println("差集：" + reduce1);
        Map<Integer, List<String>> map = new HashMap<>();
        if (reduce1.size() > 0) {
            //第一段
            if (list.get(0).equals(DateUtil.getDateByMonth(reduce1.get(0), -1))) {
                map.put(0, Arrays.asList(list.get(0)));
            } else {
                map.put(0, Arrays.asList(list.get(0), DateUtil.getDateByMonth(reduce1.get(0), -1)));
            }
            //后续分段
            for (int i = 0; i < reduce1.size(); i++) {
                String afterMonth = DateUtil.getDateByMonth(reduce1.get(i), 1);
                if (i == reduce1.size() - 1) {
                    if (afterMonth.equals(list.get(list.size() - 1))) {
                        map.put(i + 1, Arrays.asList(list.get(list.size() - 1)));
                    } else {
                        if (!list.contains(afterMonth)) {
                            map.put(i + 1, Arrays.asList(list.get(list.size() - 1)));
                        }else{
                            map.put(i + 1, Arrays.asList(afterMonth, list.get(list.size() - 1)));
                        }
                    }
                } else {
                    String beforeMonth = DateUtil.getDateByMonth(reduce1.get(i + 1), -1);
                    if (afterMonth.equals(beforeMonth)) {
                        map.put(i + 1, Arrays.asList(afterMonth));
                    } else {
                        //若list中不含间隔大于2  1,3,6 或1 3 10
                        if (!list.contains(afterMonth) || !list.contains(beforeMonth)) {
                            continue;
                        } else {
                            map.put(i + 1, Arrays.asList(afterMonth, beforeMonth));
                        }
                    }
                }
            }
        } else {
            //无差集，则无不同
            map.put(0, Arrays.asList(list.get(0), list.get(list.size() - 1)));
        }
        return map;
    }



    /**
     * 获取起始日期到结束日期列表 如:201902-201905    [201902,201903,201904,201905]
     * @param startDateStr
     * @param endDateStr
     * @return
     */
    public static List<String> getMiddleDateList(String startDateStr, String endDateStr) {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMM");
        List<String> durationStrList = new ArrayList<>();
        try {
            Date startDate = simpleDateFormat.parse(startDateStr);
            Date endDate = simpleDateFormat.parse(endDateStr);
            String durationStr = DurationFormatUtils.formatPeriod(startDate.getTime(), endDate.getTime(), "MM");
            if(StringUtils.isNotBlank(durationStr)){
                durationStrList.add(startDateStr);
               for(int i=0; i<Integer.parseInt(durationStr); i++){
                   startDateStr = getNextMonth(startDateStr);
                   durationStrList.add(startDateStr);
               }
            }
        } catch (ParseException e) {
            log.error(String.format("获取时间列表失败: 起始日期-%s,结束日期-%", startDateStr, endDateStr));
            e.printStackTrace();
        }
        return durationStrList;
    }