树形list（菜单树）递归遍历list

来源：互联网发布：双色球算法公式技巧编辑：程序博客网时间：2024/06/05 03:52

有些时候为了方便jsp展示菜单，我们一般将查询出的菜单直接遍历重组成树形，再到前端展示。废话不多说，直接贴代码。

首先要写个entity类

package com.guo.test;public class TestEntity {private int id;private String name;private int parentId;private int level;public TestEntity(int id, String name, int parentId,int level) {super();this.id = id;this.name = name;this.parentId = parentId;this.level = level;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getParentId() {return parentId;}public void setParentId(int parentId) {this.parentId = parentId;}public int getLevel() {return level;}public void setLevel(int level) {this.level = level;}@Overridepublic String toString() {return "Location [id=" + id + ", name=" + name + ", parentId=" + parentId + ", level=" + level + "]";}}

然后就是main方法了

package com.guo.test;import java.util.ArrayList;import java.util.List;public class Test {// 查询数据库菜单表中所有数据(这里模拟一个菜单表的所有数据)static int times=0;static List<TestEntity> data = new ArrayList<TestEntity>();static {TestEntity l = new TestEntity(1, "北京市", 0,1);TestEntity l2 = new TestEntity(3, "朝阳区", 1,2);TestEntity l4 = new TestEntity(5, "大郊亭中街", 3,3);TestEntity l11 = new TestEntity(12, "二号院", 5,4);TestEntity l12 = new TestEntity(13, "三号楼", 12,5);TestEntity l13 = new TestEntity(14, "四号楼", 12,5);TestEntity l5 = new TestEntity(6, "大望路", 3,3);TestEntity l6 = new TestEntity(7, "南磨房路", 3,3);TestEntity l3 = new TestEntity(4, "海淀区", 1,2);TestEntity l7 = new TestEntity(8, "唐家岭路", 4,3);TestEntity l8 = new TestEntity(9, "上地路", 4,3);TestEntity l1 = new TestEntity(2, "天津市", 0,1);TestEntity l9 = new TestEntity(10, "红桥区", 2,2);TestEntity l10 = new TestEntity(11, "北辰区", 2,2);data.add(l2);data.add(l);data.add(l1);data.add(l3);data.add(l10);data.add(l9);data.add(l5);data.add(l4);data.add(l7);data.add(l6);data.add(l8);data.add(l12);data.add(l11);data.add(l13);}public static void main(String[] args) {List<TestEntity> resultList = new ArrayList<>();System.out.println("查询前集合大小:"+data.size());long start = System.currentTimeMillis();for (TestEntity testEntity : data) {times++;if (testEntity.getParentId()==0) {//父级菜单开始添加resultList.add(testEntity);if (ifChilds(data, testEntity.getId())) {//存在子集List<TestEntity> childs = new ArrayList<>();childs = getChildList(data,testEntity.getId(),childs);resultList.addAll(childs);}}}long end = System.currentTimeMillis();System.out.println("查询后集合大小:"+resultList.size());System.out.println("查询次数:"+times+"次");System.out.println("查询耗时:"+(end-start)+"毫秒");for (TestEntity testEntity : resultList) {String s = "";for (int i = 1; i < testEntity.getLevel(); i++) {s = s + "\t";}System.out.println(s+"I____"+testEntity.getName());}}//获取父id下的子集合private static List<TestEntity> getChildList(List<TestEntity> list,int pId,List<TestEntity> reList) {for (TestEntity testEntity : list) {times++;if (testEntity.getParentId()==pId) {//查询下级菜单reList.add(testEntity);if (ifChilds(list, testEntity.getId())) {getChildList(list, testEntity.getId(), reList);}}}return reList;}//判断是否存在子集private static boolean ifChilds(List<TestEntity> list,int pId) {boolean flag = false;for (TestEntity testEntity : list) {times++;if (testEntity.getParentId()==pId) {flag=true;break;}}return flag;}}

好了，test一下，排列出了我们想要的树形list，在页面直接遍历list就可以了，就不用再去写复杂的展示了。

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