多层部门菜单树（Tree）

方法1：利用递归

下面是Dto类

public class DepartmentListDto {

    private String id;
    private String name;
    private String parentId;
    private String companyID;
    private List<DepartmentListDto> list;

    //getter、setter method ...
}

下面是接口方法

@RequestMapping("/getCompanyDeptList")
    @ResponseBody
    public MessagePacket getCompanyDeptList(HttpServletRequest request) throws ParseException{
       
        List<Department> deptsTemp = this.departmentService.getList();
        List<DepartmentListDto> depts = new ArrayList<>();
        List<DepartmentListDto> nulllist = new ArrayList<DepartmentListDto>();
        Map<String,Object> map = new HashMap<>();
        for(Department department : deptsTemp){
            DepartmentListDto departmentListDto = new DepartmentListDto();
            departmentListDto.setId(department.getId());
            departmentListDto.setName(department.getName());
            departmentListDto.setParentId(department.getParentID());
            departmentListDto.setList(nulllist);
            depts.add(departmentListDto);
            if(department.getParentID() !=null)
                map.put(department.getParentID(),department);
        }


        List<DepartmentListDto> deptList = new ArrayList<DepartmentListDto>();
        // 先找到所有的一级部门
        for (int i = 0; i < depts.size(); i++) {
            // 一级部门没有parentId
            if ("hywater".equals(depts.get(i).getParentId()) &&
                    ("003".equals(depts.get(i).getId())
                            || "004".equals(depts.get(i).getId())
                            || "005".equals(depts.get(i).getId())
                            || "006".equals(depts.get(i).getId())
                    )
            ) {
                deptList.add(depts.get(i));
            }
        }
        // 为一级部门设置子部门，getChild是递归调用的
        for (DepartmentListDto deptDto : deptList) {
            deptDto.setList(getChildList(deptDto.getId(), depts, map));
        }

        JSONObject jsonObject = new JSONObject();
        jsonObject.put("list",nlist);
        return MessagePacket.newSuccess(jsonObject, "getCompanyDeptList success");
    }

下面是获取子部门集合的递归方法

/**
*
* 递归部门
*/
private List<DepartmentListDto> getChildList(String id, List<DepartmentListDto> depts,Map<String,Object> map) {
        // 子部门
        List<DepartmentListDto> childList = new ArrayList<>();
        for (DepartmentListDto dept : depts) {
            // 遍历所有节点，将父部门id与传过来的id比较
            if (StringUtils.isNotBlank(dept.getParentId())) {
                if (dept.getParentId().equals(id)) {
                    childList.add(dept);
                }
            }
        }
        // 把子部门的子部门再循环一遍
        for (DepartmentListDto dept : childList) {// map中存在的部门还有子部门
            if (map.containsKey(dept.getId())) {
                // 递归
                dept.setList(getChildList(dept.getId(), depts,map));
            }
        } // 递归退出条件
        if (childList.size() == 0) {
            return null;
        }
        // 返回排序后的结果
        return getSortChildren(childList);
    }

下面是排序list集合的方法

/**
     * 用匿名内部类排序list--有子部门的排序放到后面
     * @param childList
     * @return
     */
    private List<DepartmentListDto> getSortChildren(List<DepartmentListDto> childList){
        Collections.sort(childList, new Comparator<DepartmentListDto>() {
            @Override
            public int compare(DepartmentListDto o1, DepartmentListDto o2) {
                if(o1.getList().size()>o2.getList().size()){
                    return 1;
                }else{
                    return -1;
                }
            }
        }) ;
        return childList;
    }

方法2：利用Map进行临时存储

package com;

import com.alibaba.fastjson.JSONObject;
import com.kingpivot.common.utils.DateUtils;
import com.kingpivot.common.utils.QueryFilter;

import java.sql.Timestamp;
import java.text.SimpleDateFormat;
import java.util.*;


public class MyTest {

    private int id;
    private int depth;
    private int pid;
    private List<MyTest> myTestList;

    public MyTest(int id,int depth,int pid){
        this.id = id;
        this.depth = depth;
        this.pid = pid;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getDepth() {
        return depth;
    }

    public void setDepth(int depth) {
        this.depth = depth;
    }

    public int getPid() {
        return pid;
    }

    public void setPid(int pid) {
        this.pid = pid;
    }

    public List<MyTest> getMyTestList() {
        return myTestList;
    }

    public void setMyTestList(List<MyTest> myTestList) {
        this.myTestList = myTestList;
    }

    @Override
    public String toString() {
        return "MyTest{" +
                "id=" + id +
                ", depth=" + depth +
                ", pid=" + pid +
                '}';
    }

    public static void main(String[] args) {

        List<MyTest> list = new ArrayList<>();
        /*
            下面模拟一些数据
        */
        for (int i = 1; i < 4; i++) {
            MyTest myTest = new MyTest(i,2,0);
            list.add(myTest);
        }
        for (int i = 10; i < 50; i++) {
            if(i < 15){
                MyTest myTest = new MyTest(i,3,1);
                list.add(myTest);
            }
            if(i >= 15 && i < 20){
                MyTest myTest = new MyTest(i,3,2);
                list.add(myTest);
            }
            if(i >= 20 && i < 25){
                MyTest myTest = new MyTest(i,3,3);
                list.add(myTest);
            }
            if(i >= 25 && i < 30){
                MyTest myTest = new MyTest(i,4,10);
                list.add(myTest);
            }
            if(i >= 30 && i < 35){
                MyTest myTest = new MyTest(i,4,15);
                list.add(myTest);
            }
            if(i >= 35 && i < 40){
                MyTest myTest = new MyTest(i,4,20);
                list.add(myTest);
            }
            if(i >= 40){
                MyTest myTest = new MyTest(i,5,35);
                list.add(myTest);
            }
        }

        /*
            下面用两个map进行临时存储
        */
        Map<Integer,List<MyTest>> map = new HashMap<>();
        Map<Integer,List<MyTest>> dmap = new HashMap<>();
        for (MyTest myTest : list) {
            List<MyTest> maplist = map.get(myTest.getPid());
            if(maplist == null){
                maplist = new ArrayList<>();
                map.put(myTest.getPid(),maplist);
            }
            maplist.add(myTest);
        }

        //移除顶级目录
        map.remove(0);

        List<MyTest> nlist = new ArrayList<>();
        for (MyTest myTest : list) {
            List<MyTest> maplist = map.get(myTest.getId());
            List<MyTest> maplist2 = map.get(myTest.getPid());
            if(maplist != null){
                myTest.setMyTestList(maplist);
            }
            if(maplist2 == null){
                nlist.add(myTest);
            }
        }
        System.out.println(JSONObject.toJSONString(nlist));
    }
}