今天遇到一个问题如下：

Paste_Image.png

Paste_Image.png

把上图的数据结构，转换成下图的数据结构。结果今天脑袋瓦特了，想了有2个小时没用想出思路。后来在网友的帮助下得到解决。
回到正题:

这是原始的数据结构：
Arera

@Data
public class Area implements Serializable {

    private String prvoince;
    private String city;
    private String district;
    private String address;

    public Area(String prvoince, String city, String district, String address) {
        this.prvoince = prvoince;
        this.city = city;
        this.district = district;
        this.address = address;
    }
}

下面是需要的辅助类

City:

@Data
public class City implements Serializable {
    private String cityName;
    private List<District> districtList;

    public void addDistrict(List<District> district) {
        for (District d : district) {
            districtList.add(d);
        }
    }

    public City(String cityName, List<District> districtList) {
        this.cityName = cityName;
        this.districtList = districtList;
    }
}

Distract:

@Data
public class District implements Serializable{
    private String districtName;
    private List<Detail> detailList;

    public void addDetail(List<Detail> detail) {
        for (Detail d : detail) {
            detailList.add(d);
        }
    }

    public District(String districtName, List<Detail> detailList) {
        this.districtName = districtName;
        this.detailList = detailList;
    }
}

Detail:

@Data
public class Detail implements Serializable {
    private String address;

    public Detail(String address) {
        this.address = address;
    }
}

下面就是开始转换数据结构的代码了，其实很简单。

public static void main(String[] args) {
        List<Area> areaList = new ArrayList<Area>();
        areaList.add(new Area("江苏省", "南京市", "玄武区", "新模范马路1001号"));
        areaList.add(new Area("江苏省", "南京市", "秦淮区", "雨花台路30号"));
        areaList.add(new Area("江苏省", "南京市", "鼓楼区", "中山1路1号"));
        areaList.add(new Area("湖南省", "长沙市", "芙蓉区", "橘子洲"));
        areaList.add(new Area("湖南省", "长沙市", "下沙区", "宝昌路32号"));
        areaList.add(new Area("江苏省", "徐州市", "云龙区", "云龙大道22号"));
        areaList.add(new Area("江苏省", "徐州市", "铜山区", "上海路45号"));

        covertData(areaList);
    }
    private static void covertData(List<Area> areaList) {
        Map<String, City> cityMap = new HashMap<>(); //最终需要的数据结构
        Map<String, District> districtMap = new HashMap<>(); //区名称的数据结构， 辅助作用
        areaList.stream().forEach(item -> {
            Detail detail = new Detail(item.getAddress());
            List<Detail> details = new ArrayList<>();
            details.add(detail);
            if (districtMap.containsKey(item.getDistrict())) {
                //如果区名称已经存在，更新区下面的详细地址
                districtMap.get(item.getDistrict()).addDetail(details);
            } else {
                //如果区名称不存在，就创建这个区并且加入map
                District district = new District(item.getDistrict(), details);
                List<District> districtList = new ArrayList<>();
                districtList.add(district);
                districtMap.put(item.getDistrict(), district);

                if (cityMap.containsKey(item.getCity())) {
                    //如果city存在，更新city下面的区
                    cityMap.get(item.getCity()).addDistrict(districtList);
                } else {
                    //如果city名称不存在，就创建这个city并加入map
                    City city = new City(item.getCity(), districtList);
                    cityMap.put(item.getCity(), city);
                }
            }
        });
        System.out.println(JSONObject.toJSONString(cityMap)); //这个就是我最终需要的结果
    }

特此记一下，说不定哪天脑子又突然瓦特了。