list转tree，用于展示层级结构

list转tree，用于展示层级结构

部门类定义

import java.util.List;

/**
* 部门类（省略get set方法）
**/
public class DepartmentVO {
   /**
    * 当前部门id
    */
   private String deptId;

   /**
    * 父部门id
    */
   private String parentId;

   /**
    * 当前部门子部门
    */
   private List<DepartmentVO> childrens;

方法的实现

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

/**
* 模拟七个部门，分三个层级
*/
public class Test4 {
   public static void main(String[] args) {
       //一级部门
       DepartmentVO level100 = new DepartmentVO();
       level100.setDeptId("10000");
       level100.setParentId("0");

       //二级部门
       DepartmentVO level200 = new DepartmentVO();
       level200.setDeptId("20000");
       level200.setParentId("10000");
       DepartmentVO level201 = new DepartmentVO();
       level201.setDeptId("20001");
       level201.setParentId("10000");
       DepartmentVO level202 = new DepartmentVO();
       level202.setDeptId("20002");
       level202.setParentId("10000");

       //三级部门
       DepartmentVO level300 = new DepartmentVO();
       level300.setDeptId("30000");
       level300.setParentId("20000");
       DepartmentVO level301 = new DepartmentVO();
       level301.setDeptId("30000");
       level301.setParentId("20000");
       DepartmentVO level302 = new DepartmentVO();
       level302.setDeptId("30000");
       level302.setParentId("20000");

       List<DepartmentVO> list = new ArrayList<>();
       list.add(level100);
       list.add(level200);
       list.add(level201);
       list.add(level202);
       list.add(level300);
       list.add(level301);
       list.add(level302);
       List<DepartmentVO> tree = getDepartmentTree(list);
   }

   /**
    *  list转tree方法
    */
   public static List<DepartmentVO> getDepartmentTree(List<DepartmentVO> list) {
       for (DepartmentVO l : list) {
              //每次循环找到每个节点的子节点们（f代表符合条件的集合），并挂载到当前节点下
           List<DepartmentVO> children = list.stream().filter(f -> l.getDeptId().equals(f.getParentId())).collect(Collectors.toList());
           l.setChildrens(children);
       }
      //for循环结束，整棵树挂载完毕，需要找到树的根节点（此例定义parentId为0就是根节点）
       List<DepartmentVO> rootNodes = list.stream()
               .filter(f -> f.getParentId() == "0" || Objects.isNull(f.getParentId())).collect(Collectors.toList());
       return rootNodes;
   }
}

最终生产的树转JSON结构如下

[
   {
       "deptId": "10000",
       "parentId": "0",
       "childrens": [
           {
               "deptId": "20000",
               "parentId": "10000",
               "childrens": [
                   {
                       "deptId": "30000",
                       "parentId": "20000",
                       "childrens": []
                   },
                   {
                       "deptId": "30000",
                       "parentId": "20000",
                       "childrens": []
                   },
                   {
                       "deptId": "30000",
                       "parentId": "20000",
                       "childrens": []
                   }
               ]
           },
           {
               "deptId": "20001",
               "parentId": "10000",
               "childrens": []
           },
           {
               "deptId": "20002",
               "parentId": "10000",
               "childrens": []
           }
       ]
   }
]