java各位数字补位，左边补0

  @Override
    @Transactional
    public CommonResult addUnit2(AddUnitReq req) {
        //社区
        QueryWrapper wrapperHouse = new QueryWrapper();
        wrapperHouse.eq("id", req.getHouseId());
        RiHouse house = riHouseMapper.selectOne(wrapperHouse);
        //楼
        QueryWrapper wrapperRiHouseFloor = new QueryWrapper();
        wrapperRiHouseFloor.eq("id", req.getFloorId());
        RiHouseFloor floor = riHouseFloorMapper.selectOne(wrapperRiHouseFloor);
        //单元
        RiHouseUnit unit = new RiHouseUnit();
        unit.setUnitName(req.getUnitName());
        unit.setHouseId(req.getHouseId());
        unit.setFloorId(req.getFloorId());
        riHouseUnitMapper.insert(unit);
        //楼层
        RiHouseLayer riHouseLayer = null;
        //户数
        RiHouseRoom riHouseRoom = null;

        StringBuilder str = new StringBuilder();
        if (req.getLayerNum() != null) {
            for (int i = req.getLayerNum();  i > 0; i--) {
                riHouseLayer = new RiHouseLayer();
                riHouseLayer.setHouseId(req.getHouseId());
                riHouseLayer.setFloorId(req.getFloorId());
                riHouseLayer.setUnitId(unit.getId());
                riHouseLayer.setLayerName((req.getLayerNum()-i)+1 + "层");
                riHouseLayer.setLayerSort(i-1);
                riHouseLayerMapper.insert(riHouseLayer);
                str.append((req.getLayerNum()-i)+1 + "层");
                str.append(",");
                List   roomList=    new ArrayList<>();
                if (req.getRoomNum() != null) {//每层每户
                    for (int i2 = 1; i2 < req.getRoomNum() + 1; i2++) {
                        riHouseRoom = new RiHouseRoom();
                        riHouseRoom.setHouseId(req.getHouseId());
                        riHouseRoom.setFloorId(req.getFloorId());
                        riHouseRoom.setUnitId(unit.getId());
                        riHouseRoom.setLayerId(riHouseLayer.getId());
                        riHouseRoom.setRoomCode("户室" + i2);
                        //这里户室需要个位数补位
                        riHouseRoom.setRoomName(((req.getLayerNum()-i)+1)+ "层"+ String.format("%02d", i2));
                        roomList.add(riHouseRoom);
                    }
                    riHouseRoomService.saveBatch(roomList);

                } else {//每层一户
                    riHouseRoom = new RiHouseRoom();
                    riHouseRoom.setHouseId(req.getHouseId());
                    riHouseRoom.setFloorId(req.getFloorId());
                    riHouseRoom.setUnitId(unit.getId());
                    riHouseRoom.setLayerId(riHouseLayer.getId());
                    riHouseRoom.setRoomCode("户室1");
                    riHouseRoom.setRoomName(((req.getLayerNum()-i)+1)+"层01");
                    riHouseRoomMapper.insert(riHouseRoom);
                }
            }
        } else {//默认一层一户
            //楼层
            riHouseLayer = new RiHouseLayer();
            riHouseLayer.setHouseId(req.getHouseId());
            riHouseLayer.setFloorId(req.getFloorId());
            riHouseLayer.setUnitId(unit.getId());
            riHouseLayer.setLayerName("1层");
            riHouseLayer.setLayerSort(0);
            riHouseLayerMapper.insert(riHouseLayer);
            str.append("1层");
            str.append(",");
            //户数
            riHouseRoom = new RiHouseRoom();
            riHouseRoom.setHouseId(req.getHouseId());
            riHouseRoom.setFloorId(req.getFloorId());
            riHouseRoom.setUnitId(unit.getId());
            riHouseRoom.setLayerId(riHouseLayer.getId());
            riHouseRoom.setRoomCode("户室1");
            riHouseRoom.setRoomName("1层01");
            riHouseRoomMapper.insert(riHouseRoom);
        }

        //待确认
        UpdateWrapper wrapperRiHouse = new UpdateWrapper<>();
        wrapperRiHouse.eq("id", req.getHouseId()).set("read_flag", false);
        riHouseMapper.update(null, wrapperRiHouse);
        RiHouseUnitAddResp resp = new RiHouseUnitAddResp();
        resp.setId(unit.getId());
        return CommonResult.success(resp);
    }

方法

1.通过 String.format 方式来进行左位补零操作

// 1为 int 类型、0代表前面要补位的字符、2代表字符串的长度、d表示参数为整数类型
String s = String.format("%02d", 1);//1，是自己传的参数
System.out.println(s);

2.通过 NumberFormat 方式来进行左位补零操作

// 首先通过 getInstance 创建一个 NumberFormat 实例
NumberFormat numberFormat = NumberFormat.getInstance();
// 设置最大和最小整数位数
numberFormat.setMaximumIntegerDigits(2);
numberFormat.setMinimumIntegerDigits(2);
// 最后通过 format 方法操作要补零的数字即可
System.out.println(numberFormat.format(2));