lambda表达式解决java后台分组排序过程解析

/**
   *
   * @param startTime 开始时间
   * @param endTime  结束时间
   * @param tbOrderExecutionExample 模糊查询
   * @return 结果集
   * @throws ParseException 转换异常
   */
  private Map<String, List<TBOrderExecution>> getListMap(@RequestParam(value = "startTime", required = false) String startTime, @RequestParam(value = "endTime", required = false) String endTime, TBOrderExecutionExample tbOrderExecutionExample) throws ParseException {
    List<TBOrderExecution> list = tbDocOrderAdmissionService.selectByExample(tbOrderExecutionExample);
    //获取时间段分组
    SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd");
    List<String> lists = DateRangUtil.getAllDate(startTime, endTime);
    Map<String, List<TBOrderExecution>> map = list.stream().collect(Collectors.groupingBy(x -> sdf2.format(x.getYzjhksrq())));
    Set<String> keys = map.keySet();
    Map<String, List<TBOrderExecution>> finalMap = map;
    lists.forEach(ele -> {
      if (!keys.contains(ele)) {
        finalMap.put(ele, null);
      }

    });
    Map<String, List<TBOrderExecution>> finalMaps = new LinkedHashMap<>();
    Set<String> strings = finalMap.keySet();
    List<String> dates = new ArrayList<>(strings);
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    Collections.sort(dates, new Comparator<String>() {
      DateFormat f = new SimpleDateFormat("yyyy-MM-dd");

      @Override
      public int compare(String o1, String o2) {
        try {
          return f.parse(o1).compareTo(f.parse(o2));
        } catch (ParseException e) {
          throw new IllegalArgumentException(e);
        }
      }
    });
    dates.forEach(ele -> {
      finalMap.forEach((key, value) -> {
        if (key.equals(ele)) {
          finalMaps.put(ele, value);
        }
      });
    });
    return finalMaps;
  }

public static List<String> getAllDate(String start, String end) throws ParseException {
    List<Date> lDate = new ArrayList<>();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    Date dBegin = sdf.parse(start);
    Date dEnd = sdf.parse(end);

    lDate.add(dBegin);
    Calendar calBegin = Calendar.getInstance();
    // 使用给定的 Date 设置此 Calendar 的时间
    calBegin.setTime(dBegin);
    Calendar calEnd = Calendar.getInstance();
    // 使用给定的 Date 设置此 Calendar 的时间
    calEnd.setTime(dEnd);
    // 测试此日期是否在指定日期之后
    while (dEnd.after(calBegin.getTime())) {
      // 根据日历的规则，为给定的日历字段添加或减去指定的时间量
      calBegin.add(Calendar.DAY_OF_MONTH, 1);
      lDate.add(calBegin.getTime());
    }
    List<String> allDate = new ArrayList<>();
    lDate.forEach(ele -> allDate.add(sdf.format(ele)));
    return allDate;

  }