树形结构设计总结，对于像部门，权限这样

1.树形结构三要素：
parentId：父节点id；
level：设计模式父节点的id+level。顶级节点的level默认值0；
seq:同一层级排序。
2.遍历：
主要思路：同一层级的节点保存在key为level的map结构中。这样就可以通过level拿到所有的子节点。
3.树形结构修改
1是root节点，1下有两个节点2，3。2下有一个节点4。4下有一个节点5.
那么修改规则如下：将4放到3下面。同时更新4的子节点的level。
思路：
(1)创建两个对象before,after来分别表示更新之前4的信息。
before:0.1.2 after 0.1.3
(2)通过before的id拿到ParentId为id的所有子节点。
(3)遍历自己点集合。
  将子节点的level的前缀删除了before的level剩下就是层次结构中不动的部分 childLevel。
 newLevel = after.getLevel()+childLevel；即最新的level。
 子节点5level 0.1.2.4。删除修改之前父节点level。剩下4；
 4结合修改之后的Level即0.1.3生成新的level：0.1.3.4即最新level.

package com.lai.tree.service;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

import org.apache.commons.collections.CollectionUtils;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;
import com.lai.tree.common.LevelUtil;
import com.lai.tree.pojo.Dept;
import com.lai.tree.pojo.DeptLevelDto;

public class DeptService {

public static void main(String[] args) throws Exception {
DeptService deptService = new DeptService();
//		getLevelDept(deptService);

changeLevelDept(deptService);

//		deleteLevelDept(deptService);
}

private static void changeLevelDept(DeptService deptService) throws Exception {
List<Dept> levelDeptList = deptService.getLevelDept();
//将id为4的部门挂到id为1上面
Dept parentDept = new Dept();
parentDept.setId(1);
parentDept.setLevel(LevelUtil.ROOT);

Dept before =  deptService.getLevelDeptById(4);
DeptLevelDto after = new DeptLevelDto();
after.setId(4);
after.setParentId(1);
after.setLevel(LevelUtil.calculateLevel(parentDept.getLevel(), parentDept.getId()));
List<Dept> childDeptList = deptService.getChildLevelDept();
for (Dept  dept: childDeptList) {
String beforeLevel = dept.getLevel();
if(beforeLevel.indexOf(before.getLevel()) == 0) {
String subLevel = beforeLevel.substring(before.getLevel().length());
dept.setLevel(after.getLevel() + subLevel);
}
}
Multimap<String, DeptLevelDto> levelDeptMap = ArrayListMultimap.create();
List<DeptLevelDto> rootDeptList = new ArrayList<>();
rootDeptList.add(after);
DeptLevelDto deptDto = null;
for (Dept dept : childDeptList) {
deptDto = DeptLevelDto.adapt(dept);
levelDeptMap.put(dept.getLevel(), deptDto);
}
deptService.listToTree(rootDeptList, levelDeptMap);
System.out.println(new ObjectMapper().writeValueAsString(rootDeptList));
}

private List<Dept> getChildLevelDept() {
List<Dept> deptList = new ArrayList<>();
Dept dept = new Dept();
dept.setId(5);
dept.setParentId(4);
dept.setSeq(0);
dept.setName("level3.0");
dept.setLevel(LevelUtil.calculateLevel("0.1.2", 4));
deptList.add(dept);

dept = new Dept();
dept.setId(6);
dept.setParentId(4);
dept.setSeq(0);
dept.setName("level3.1");
dept.setLevel(LevelUtil.calculateLevel("0.1.2", 4));
deptList.add(dept);
return deptList;
}

private Dept getLevelDeptById(int i) {
Dept dept = new Dept();
dept.setId(4);
dept.setParentId(2);
dept.setSeq(0);
dept.setName("level2.0");
dept.setLevel(LevelUtil.calculateLevel("0.1", 2));
return dept;
}

private static void getLevelDept(DeptService deptService) throws JsonProcessingException {
List<Dept> deptList = deptService.getLevelDept();
/**
* key是level，value是同一层次的部门对象集合
*/
Multimap<String, DeptLevelDto> levelDeptMap = ArrayListMultimap.create();

List<DeptLevelDto> rootDeptList = new ArrayList<DeptLevelDto>();
DeptLevelDto deptDto = null;

for (Dept dept : deptList) {
deptDto = DeptLevelDto.adapt(dept);
levelDeptMap.put(dept.getLevel(), deptDto);
if(deptDto.getLevel().equals(LevelUtil.ROOT)) {
rootDeptList.add(deptDto);
}
}
deptService.listToTree(rootDeptList, levelDeptMap);
ObjectMapper objectMapper = new ObjectMapper();
String deptTreeJson = objectMapper.writeValueAsString(rootDeptList);
System.out.println(deptTreeJson);
}
/**
* 遍历同一层级的dept,从Multimap中拿到其下一集的dept并且放到deptDto的deptList中
* @param parentDeptList
* @param root
* @param levelDeptMap
*/
public void listToTree(List<DeptLevelDto> parentDeptList, Multimap<String, DeptLevelDto> levelDeptMap) {
List<DeptLevelDto> deptLevelDtoList = null;
if(CollectionUtils.isNotEmpty(parentDeptList)) {
Collections.sort(parentDeptList, deptSeqComparator);
//遍历同一层级的dept
for (DeptLevelDto deptLevelDto : parentDeptList) {
String parentLevel = deptLevelDto.getLevel();
Integer parentId = deptLevelDto.getId();
deptLev
4000
elDtoList = (List<DeptLevelDto>)levelDeptMap.get(LevelUtil.calculateLevel(parentLevel, parentId));
deptLevelDto.setDeptList(deptLevelDtoList);
listToTree(deptLevelDtoList, levelDeptMap);
}
}
}

public Comparator<DeptLevelDto> deptSeqComparator = new Comparator<DeptLevelDto>() {
@Override
public int compare(DeptLevelDto o1, DeptLevelDto o2) {
return o1.getSeq() - o2.getSeq();
}
};

private void testCountLevel() {
String calculateLevel = LevelUtil.calculateLevel("1", 1);
System.out.println(calculateLevel);
}

public List<Dept> getLevelDept() {
List<Dept> deptList = new ArrayList<Dept>();
Dept dept = new Dept();
dept.setId(1);
dept.setParentId(0);
dept.setSeq(0);
dept.setName("root");
dept.setLevel(LevelUtil.ROOT);
deptList.add(dept);

dept = new Dept();
dept.setId(2);
dept.setParentId(1);
dept.setSeq(0);
dept.setName("level1.0");
dept.setLevel(LevelUtil.calculateLevel("0", 1));
deptList.add(dept);

dept = new Dept();
dept.setId(3);
dept.setParentId(1);
dept.setSeq(1);
dept.setName("level1.1");
dept.setLevel(LevelUtil.calculateLevel("0", 1));
deptList.add(dept);

dept = new Dept();
dept.setId(4);
dept.setParentId(2);
dept.setSeq(0);
dept.setName("level2.0");
dept.setLevel(LevelUtil.calculateLevel("0.1", 2));
deptList.add(dept);

dept = new Dept();
dept.setId(5);
dept.setParentId(4);
dept.setSeq(0);
dept.setName("level3.0");
dept.setLevel(LevelUtil.calculateLevel("0.1.2", 4));
deptList.add(dept);

dept = new Dept();
dept.setId(6);
dept.setParentId(4);
dept.setSeq(0);
dept.setName("level3.1");
dept.setLevel(LevelUtil.calculateLevel("0.1.2", 4));
deptList.add(dept);
return deptList;
}
}

源码 http://download.csdn.net/download/u014172271/10268699