Java根据年度将数据分组

现在有这么一组数据

code                   name                year

45615654           x1                     2018-2019

78912648           x2                     2018-2019

42364322           x3                     2017-2018

87635225           x4                     2016-2017

我想在Java后台将数据按year分组该怎么做呢

首先数据一定是根据year排序好的

最后返到前台的数据格式是这样的

原理就是year每换一次map就往里put一组year和list

chargeList: [
          {
            year: 2018-2019,
            list: [
              {
                code: 45615654,
                name: "x1"
              },
              {
                code: 78912648,
                name: "x2"
              },
            ]
          }
        ]

第一种实现：

想要获得这样的数据需要最外层循环根据不重复year的个数来循环

内层再根据year来判断将什么数据放到list中

最后将year和list装在dataMap里

List<ClientResult> clientMsts = clientMstMapper.selectHeatingData2();
List<Map> dataList = new ArrayList<>();
        String year = "";
        List<String> yearList = new ArrayList<>();
        for (ClientResult c : clientMsts) {
            if (!year.equals(c.getYear())) {
                year = c.getYear();
                yearList.add(year);
            }
        }
        for (int i = 0; i < yearList.size(); i++) {
            Map<String, Object> map = new HashMap<>();//装的是code和name
            Map<String, Object> dataMap = new HashMap<>();//装year和list
            List<Map> list = new ArrayList<>();
            year = yearList.get(i);
            for (ClientResult c : clientMsts) {
                if (year.equals(c.getYear())) {
                    map.put("code", c.getCode());
                    map.put("name", c.getName());
                    list.add(map);
                }
            }
            dataMap.put("year", year);
            dataMap.put("list", list);
            dataList.add(dataMap);
        }
        Map<String, Object> map = new HashMap<>();
        map.put("dataList", dataList);

第二种实现：

当year不相同的时候往dataMap中put一组数据

List<ClientResult> clientMsts = clientMstMapper.selectHeatingData2();
        List<Map> dataList = new ArrayList<>();
        String year = "";
        List<Map> lists = null;
        for (ClientResult c : clientMsts) {
            Map<String, Object> dataMap= new HashMap<>();
            boolean a = false;
            if (!year.equals(c.getClientPaymentYear())) {
                year = c.getClientPaymentYear();
                dataMap.put("year", year);
                lists = new ArrayList<>();
                a = true;
            }
            Map map = new HashMap();
            map.put("code", c.getClientMstCode());
            map.put("name", c.getHousingEstateName());
            lists.add(map2);
            if (a) {
                dataMap.put("data", lists);
                dataList.add(map);
            }
        }
        Map<String, Object> map = new HashMap<>();
        map.put("dataList", dataList);

这就是Java后台根据年度分组的详细过程，可能还有别的更好地办法，欢迎一起讨论