# 多级菜单数据结构 - 非递归

创建数据库表：

	/*
	Navicat Premium Data Transfer

	Source Server : windows
	Source Server Type : MySQL
	Source Server Version : 80028
	Source Host : localhost:3306
	Source Schema : tree_data

	Target Server Type : MySQL
	Target Server Version : 80028
	File Encoding : 65001

	Date: 29/02/2024 11:26:32
	*/

	SET NAMES utf8mb4;
	SET FOREIGN_KEY_CHECKS = 0;

	-- ----------------------------
	-- Table structure for data_one
	-- ----------------------------
	DROP TABLE IF EXISTS `data_one`;
	CREATE TABLE `data_one` (
	`id` int NOT NULL AUTO_INCREMENT,
	`name` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL DEFAULT '',
	`p_id` int NULL DEFAULT NULL,
	`order_num` int NULL DEFAULT NULL,
	PRIMARY KEY (`id`) USING BTREE
	) ENGINE = InnoDB AUTO_INCREMENT = 7 CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

	-- ----------------------------
	-- Records of data_one
	-- ----------------------------
	INSERT INTO `data_one` VALUES (1, '邢台', 0, 1);
	INSERT INTO `data_one` VALUES (2, '沙河市', 1, 2);
	INSERT INTO `data_one` VALUES (3, '河北省', 1, 3);
	INSERT INTO `data_one` VALUES (4, '北京 ', 0, 1);
	INSERT INTO `data_one` VALUES (5, '朝阳', 4, 2);
	INSERT INTO `data_one` VALUES (6, '赞善乡', 2, 1);

	SET FOREIGN_KEY_CHECKS = 1;

创建好表如下：

编写 java 代码：

实体类：

	public class DataOne {
	private Integer id;
	private String name;
	private Integer pId;
	private Integer orderNum; // 排序字段
	private List<DataOne> data1s; // 子级菜单集合

	public List<DataOne> getData1s() {
	return data1s;
	}

	public void setData1s(List<DataOne> data1s) {
	this.data1s = data1s;
	}

	public Integer getId() {
	return id;
	}

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

	public String getName() {
	return name;
	}

	public void setName(String name) {
	this.name = name;
	}

	public Integer getpId() {
	return pId;
	}

	public void setpId(Integer pId) {
	this.pId = pId;
	}

	public Integer getOrderNum() {
	return orderNum;
	}

	public void setOrderNum(Integer orderNum) {
	this.orderNum = orderNum;
	}

	@Override
	public String toString() {
	return "Data1{" +
	"id=" + id +
	", name='" + name + '\'' +
	", pId=" + pId +
	", orderNum=" + orderNum +
	", data1s=" + data1s +
	'}';
	}
	}

创建 JdbcUtils 工具类：

	public class JUtils {

	private static DataSource source;
	static{
	Properties pro = null;
	try{
	pro = new Properties();
	InputStream in = JUtils.class.getClassLoader().getResourceAsStream("druid.properties");
	pro.load(in);
	source = DruidDataSourceFactory.createDataSource(pro);
	}catch(IOException e){
	throw new RuntimeException(e);
	} catch (Exception e) {
	e.printStackTrace();
	}
	}
	public static Connection getConnection() throws SQLException {
	return source.getConnection();
	}
	public static DataSource getSource() {
	return source;
	}
	}

创建查询数据库并返回多级菜单数据结构的类：

	public class TreeDataOne {
	// 创建 JdbcTemplate 对象查询数据库
	private JdbcTemplate jdbcTemplate = new JdbcTemplate(JUtils.getSource());

	public List<DataOne> getTreeChildren() {
	// 查询 data_one 表的所有数据
	String sql = "select * from data_one";
	List<DataOne> query = jdbcTemplate.query(sql, new BeanPropertyRowMapper<DataOne>(DataOne.class));
	// 调用函数将所有数据根据某字段来构建成树形结构并返回
	return buildTree(query);
	}

	public List<DataOne> buildTree(List<DataOne> listTree) {
	// 创建 map 集合
	Map<Integer, DataOne> map = new HashMap<>();
	for (DataOne datas : listTree) {
	// 存储每条数据的 id 与它的数据
	map.put(datas.getId(), datas);
	}
	// 创建 List 集合
	List<DataOne> datalists = new ArrayList<>();
	for (DataOne data1 : listTree) {
	// 获取遍历的每条数据的 pId
	Integer parentId = data1.getpId();
	if (parentId == null \|\| parentId == 0) {
	datalists.add(data1);
	}else {
	DataOne dataOne = map.get(parentId);
	if (dataOne != null) {
	if (dataOne.getData1s() == null) {
	dataOne.setData1s(new ArrayList<>());
	}
	dataOne.getData1s().add(data1);
	}
	}
	}
	sortTree(datalists);
	return datalists;
	}

	public void sortTree(List<DataOne> listTree) {
	for (DataOne datas : listTree) {
	if (datas.getData1s() != null && ! datas.getData1s().isEmpty()) {
	sortTree(datas.getData1s());
	}
	}
	Collections.sort(listTree, Comparator.comparingInt(DataOne::getOrderNum));
	}
	}

测试代码：

	// 多级菜单数据测试
	@Test
	public void testTwo() {
	TreeDataOne data1Service = new TreeDataOne();
	List<DataOne> treeChildren = data1Service.getTreeChildren();
	for (DataOne treeChild : treeChildren) {
	System.out.println(treeChild);
	}
	}

打印结果：

信息: {dataSource-1} inited
Data1{id=1, name='邢台', pId=0, orderNum=1, data1s=[Data1{id=2, name='沙河市', pId=1, orderNum=2, data1s=[Data1{id=6, name='赞善乡', pId=2, orderNum=1, data1s=null}]}, Data1{id=3, name='河北省', pId=1, orderNum=3, data1s=null}]}
Data1{id=4, name='北京 ', pId=0, orderNum=1, data1s=[Data1{id=5, name='朝阳', pId=4, orderNum=2, data1s=null}]}

格式化后的数据：

	Data1 {
	id = 1, name = '邢台', pId = 0, orderNum = 1, data1s = [Data1 {
	id = 2, name = '沙河市', pId = 1, orderNum = 2, data1s = [Data1 {
	id = 6, name = '赞善乡', pId = 2, orderNum = 1, data1s = null
	}]
	}, Data1 {
	id = 3, name = '河北省', pId = 1, orderNum = 3, data1s = null
	}]
	}
	Data1 {
	id = 4, name = '北京 ', pId = 0, orderNum = 1, data1s = [Data1 {
	id = 5, name = '朝阳', pId = 4, orderNum = 2, data1s = null
	}]
	}

计算机学科案例Demo 菜单数据结构

# 多级菜单数据结构 - 非递归

二级菜单数据结构

JdbcTemplate详解