Java根據年度將數據分組

現在有這么一組數據

code	name	year
45615654	x1	2018-2019
78912648	x2	2018-2019
42364322	x3	2017-2018
87635225	x4	2016-2017

我想在Java后台將數據按year分組該怎么做呢

首先數據一定是根據year排序好的

最后返到前台的數據格式是這樣的

原理就是year每換一次map就往里put一組year和list

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

第一種實現

想要獲得這樣的數據需要最外層循環根據不重復year的個數來循環

內層再根據year來判斷將什么數據放到list中

最后將year和list裝在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<>();//裝的是code和name
            Map<String, Object> dataMap = new HashMap<>();//裝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);

第二種實現

當year不相同的時候往dataMap中put一組數據

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(map);
            if (a) {
                dataMap.put("data", lists);
                dataList.add(map);
            }
        }
        Map<String, Object> map = new HashMap<>();
        map.put("dataList", dataList);

這就是Java后台根據年度分組的詳細過程，可能還有別的更好地辦法，歡迎一起討論