跟网上的不同的是，我这种方式是以时间换空间的做法，不会一次性把数据全查出来再慢慢遍历，而是每次查询是否存在子级，有就递归下去查。
数据量大时，查库的次数比较多，数据量少时对数据库查询次数少，压力较小，但是多次查询不会出现一次查询数据量很大卡住的情况。
思路
- 先获取一级菜单，对每个一级菜单设子区域。
- 如果子区域还有子区域，就递归查询，直到查不到子区域返回。
- 递归的核心就是在方法中设置一个返回条件，防止无限递归下去。
* @author liukai
* @since 2019/6/12 16:14.
*/
public class SignTree {
private static RegionDao regionDao = new RegionDao();
public static void main(String[] args) {
//1. 先拿到第一级地址
//2. 递归查每一级下面的子级：
// 如果子级下面，还有子级就递归
// 如果子级下面，没有子级就返回退出递归
List<RegionBean> firstRegion = regionDao.queryParentId(0);
for (RegionBean regionBean : firstRegion) {
//设置子区域
regionBean.setRegionBeanList(setChild(regionBean.getId()));
}
String jsonObject = JSONObject.toJSONString(firstRegion);
System.out.println(jsonObject);
}
/**
* 递归查询所有子级
* @param parentId
* @return
*/
private static List<RegionBean> setChild(int parentId) {
List<RegionBean> childList = new ArrayList<>();
List<RegionBean> childTemp = regionDao.queryParentId(parentId);
if (childTemp != null && childTemp.size() > 0) {
for (RegionBean regionBean : childTemp) {
childList.add(regionBean);
regionBean.setRegionBeanList(setChild(regionBean.getId()));
}
} else {
return childList;
}
return childList;
}
}
class RegionDao {
/**
* 查询父级
* @param parentId
* @return
*/
public List<RegionBean> queryParentId(int parentId) {
List<RegionBean> regionBeans = dataBaseRegion();
List<RegionBean> firstRegion = new ArrayList<>();
for (RegionBean regionBean : regionBeans) {
if (regionBean.getParentId() == parentId) {
firstRegion.add(regionBean);
}
}
return firstRegion;
}
public static List<RegionBean> dataBaseRegion() {
List<RegionBean> regionBeans = Arrays.asList(
new RegionBean(2, "北京市", "北京市", 0, 1),
new RegionBean(22, "天津市", "天津市", 0, 2),
new RegionBean(783, "上海市", "上海市", 0, 3),
new RegionBean(457, "辽宁省", "辽宁省", 0, 8),
new RegionBean(458, "沈阳市", "辽宁省-沈阳市", 457, 1),
new RegionBean(472, "铁岭市", "辽宁省-铁岭市", 457, 2),
new RegionBean(480, "大连市", "辽宁省-大连市", 457, 3),
new RegionBean(491, "鞍山市", "辽宁省-鞍山市", 457, 4),
new RegionBean(499, "抚顺市", "辽宁省-抚顺市", 457, 5),
new RegionBean(507, "本溪市", "辽宁省-本溪市", 457, 6),
new RegionBean(514, "丹东市", "辽宁省-丹东市", 457, 7),
new RegionBean(521, "锦州市", "辽宁省-锦州市", 457, 8),
new RegionBean(529, "营口市", "辽宁省-营口市", 457, 9),
new RegionBean(536, "阜新市", "辽宁省-阜新市", 457, 10),
new RegionBean(544, "辽阳市", "辽宁省-辽阳市", 457, 11),
new RegionBean(552, "朝阳市", "辽宁省-朝阳市", 457, 12),
new RegionBean(560, "盘锦市", "辽宁省-盘锦市", 457, 13),
new RegionBean(561, "三级数据", "辽宁省-三级数据", 560, 13),
new RegionBean(562, "三级数据", "辽宁省-三级数据", 560, 13),
new RegionBean(563, "三级数据", "辽宁省-三级数据", 560, 13),
new RegionBean(564, "三级数据", "辽宁省-三级数据", 560, 13),
new RegionBean(565, "三级数据", "辽宁省-三级数据", 560, 13),
new RegionBean(566, "三级数据", "辽宁省-三级数据", 560, 13),
new RegionBean(666, "四级数据", "辽宁省-四级数据", 566, 13)
);
return regionBeans;
}
}
public class RegionBean implements java.io.Serializable {
private static final long serialVersionUID = 1L;
private int id;
private String label;
private String fullLabel;
private int parentId;
private int sortId;
private List<RegionBean> regionBeanList = new ArrayList<>();
结果
[{"fullLabel":"北京市","id":2,"label":"北京市","parentId":0,"regionBeanList":[],"sortId":1},{"fullLabel":"天津市","id":22,"label":"天津市","parentId":0,"regionBeanList":[],"sortId":2},{"fullLabel":"上海市","id":783,"label":"上海市","parentId":0,"regionBeanList":[],"sortId":3},{"fullLabel":"辽宁省","id":457,"label":"辽宁省","parentId":0,"regionBeanList":[{"fullLabel":"辽宁省-沈阳市","id":458,"label":"沈阳市","parentId":457,"regionBeanList":[],"sortId":1},{"fullLabel":"辽宁省-铁岭市","id":472,"label":"铁岭市","parentId":457,"regionBeanList":[],"sortId":2},{"fullLabel":"辽宁省-大连市","id":480,"label":"大连市","parentId":457,"regionBeanList":[],"sortId":3},{"fullLabel":"辽宁省-鞍山市","id":491,"label":"鞍山市","parentId":457,"regionBeanList":[],"sortId":4},{"fullLabel":"辽宁省-抚顺市","id":499,"label":"抚顺市","parentId":457,"regionBeanList":[],"sortId":5},{"fullLabel":"辽宁省-本溪市","id":507,"label":"本溪市","parentId":457,"regionBeanList":[],"sortId":6},{"fullLabel":"辽宁省-丹东市","id":514,"label":"丹东市","parentId":457,"regionBeanList":[],"sortId":7},{"fullLabel":"辽宁省-锦州市","id":521,"label":"锦州市","parentId":457,"regionBeanList":[],"sortId":8},{"fullLabel":"辽宁省-营口市","id":529,"label":"营口市","parentId":457,"regionBeanList":[],"sortId":9},{"fullLabel":"辽宁省-阜新市","id":536,"label":"阜新市","parentId":457,"regionBeanList":[],"sortId":10},{"fullLabel":"辽宁省-辽阳市","id":544,"label":"辽阳市","parentId":457,"regionBeanList":[],"sortId":11},{"fullLabel":"辽宁省-朝阳市","id":552,"label":"朝阳市","parentId":457,"regionBeanList":[],"sortId":12},{"fullLabel":"辽宁省-盘锦市","id":560,"label":"盘锦市","parentId":457,"regionBeanList":[{"fullLabel":"辽宁省-三级数据","id":561,"label":"三级数据","parentId":560,"regionBeanList":[],"sortId":13},{"fullLabel":"辽宁省-三级数据","id":562,"label":"三级数据","parentId":560,"regionBeanList":[],"sortId":13},{"fullLabel":"辽宁省-三级数据","id":563,"label":"三级数据","parentId":560,"regionBeanList":[],"sortId":13},{"fullLabel":"辽宁省-三级数据","id":564,"label":"三级数据","parentId":560,"regionBeanList":[],"sortId":13},{"fullLabel":"辽宁省-三级数据","id":565,"label":"三级数据","parentId":560,"regionBeanList":[],"sortId":13},{"fullLabel":"辽宁省-三级数据","id":566,"label":"三级数据","parentId":560,"regionBeanList":[{"fullLabel":"辽宁省-四级数据","id":666,"label":"四级数据","parentId":566,"regionBeanList":[],"sortId":13}],"sortId":13}],"sortId":13}],"sortId":8}]
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