Recursive query of multi-level menu data

1. Prepare tables and data

DROP TABLE IF EXISTS `sys_menu_test`;
CREATE TABLE `sys_menu_test`  (
  `id` bigint NOT NULL AUTO_INCREMENT COMMENT ' classification id',
  `name` char(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT ' Category name ',
  `pId` bigint NULL DEFAULT NULL COMMENT ' Parent classification id',
  `showStatus` tinyint NULL DEFAULT 1 COMMENT ' Whether or not shown [0- No display ,1 Show ]',
  `sort` int NULL DEFAULT 0 COMMENT ' Sort ',
  `icon` char(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT ' Icon address ',
  PRIMARY KEY (`id`) USING BTREE,
  INDEX `pId_index`(`pId`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1437 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = ' Menu information table ' ROW_FORMAT = DYNAMIC;

-- ----------------------------
-- Records of sys_menu_test
-- ----------------------------
INSERT INTO `sys_menu_test` VALUES (1, ' China ', 0, 1, 1, NULL);
INSERT INTO `sys_menu_test` VALUES (2, ' The United States ', 0, 1, 2, NULL);
INSERT INTO `sys_menu_test` VALUES (3, ' Canada ', 0, 1, 3, NULL);
INSERT INTO `sys_menu_test` VALUES (4, ' Anhui Province ', 1, 1, 1, NULL);
INSERT INTO `sys_menu_test` VALUES (5, ' Jiangsu Province ', 1, 1, 2, NULL);
INSERT INTO `sys_menu_test` VALUES (6, ' Zhejiang Province ', 1, 1, 3, NULL);
INSERT INTO `sys_menu_test` VALUES (7, ' Xuzhou City ', 5, 1, 1, NULL);
INSERT INTO `sys_menu_test` VALUES (8, ' Hefei ', 4, 1, 1, NULL);
INSERT INTO `sys_menu_test` VALUES (9, ' Lu'an City ', 4, 1, 2, NULL);
INSERT INTO `sys_menu_test` VALUES (10, ' Jin'an District ', 9, 1, 1, NULL);
INSERT INTO `sys_menu_test` VALUES (11, ' Yu'an District ', 9, 1, 2, NULL);
INSERT INTO `sys_menu_test` VALUES (12, ' High-tech zone ', 8, 1, 3, NULL);
INSERT INTO `sys_menu_test` VALUES (13, ' Sungang town ', 10, 1, 1, NULL);
INSERT INTO `sys_menu_test` VALUES (14, ' Chunshu town ', 10, 1, 2, NULL);
INSERT INTO `sys_menu_test` VALUES (15, ' Shuxi Lake ', 12, 1, 3, NULL);
INSERT INTO `sys_menu_test` VALUES (16, ' hangzhou ', 6, 1, 1, NULL);
INSERT INTO `sys_menu_test` VALUES (17, ' lake ', 16, 1, 1, NULL);
INSERT INTO `sys_menu_test` VALUES (18, ' Lingyin Temple ', 17, 1, 1, NULL);

2. Create entity class

package com.mozheng.manageframe.entity;

import lombok.Data;
import lombok.ToString;

import java.util.List;

/** * @Description:  Menu entity class  * @Author yizhixiansheng * @Date 2021/6/30 */
@Data
@ToString
public class MenuTest{
    

    private static final long serialVersionUID = 1L;

    /** *  menu id */
    private Long id;

    /** *  Menu name  */
    private String name;

    /** *  Parent menu id */
    private Long pId;

    /** *  Whether or not shown [0- No display ,1 Show ] */
    private Integer showStatus;

    /** *  Sort  */
    private Integer sort;

    /** *  Icon address  */
    private String icon;

    /** *  Submenu collection  */
    private List<MenuTest> children;
}

3. establish sql Query statement xml file

<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.mozheng.manageframe.mapper.MenuMapper">
    <!--  Query all  -->
    <select id="listInfo" resultType="com.mozheng.manageframe.entity.MenuTest">
		select id,`name`,pId,showStatus,sort,icon from sys_menu_test
	</select>
</mapper>

4. establish mapper Interface

package com.mozheng.manageframe.mapper;

import com.mozheng.manageframe.entity.MenuTest;
import org.apache.ibatis.annotations.Mapper;
import java.util.List;

@Mapper
public interface MenuMapper {
    
    List<MenuTest> listInfo();
}

5. Create business layer interface

package com.mozheng.manageframe.service;

import com.mozheng.manageframe.entity.MenuTest;
import java.util.List;

public interface MenuService {
    
    List<MenuTest> listInfo();
}

6. Create a business layer interface implementation class

package com.mozheng.manageframe.service.Impl;

import com.mozheng.manageframe.entity.MenuTest;
import com.mozheng.manageframe.mapper.MenuMapper;
import com.mozheng.manageframe.service.MenuService;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import javax.annotation.Resource;
import java.util.*;
import java.util.stream.Collectors;

@Service
@Transactional
public class MenuServiceImpl implements MenuService {
    
    @Override
    public List<MenuTest> listInfo() {
    
        //  Get all menus 
        List<MenuTest> allMenu = menuMapper.listInfo();
        //  Get all parent nodes as 0 The node of , Root node 
        List<MenuTest> rootMenu = allMenu
                .stream()
                .filter(item -> item.getPId().equals(0L))
                .collect(Collectors.toList());
        //  Set submenu for root menu 
        rootMenu.forEach(menuTest -> menuTest.setChildren(getChildList(menuTest.getId(), allMenu)));
        //  Sort according to the order field 
        rootMenu.sort(Comparator.comparing(MenuTest::getSort));
        return rootMenu;
    }

    /** *  according to  id, Get its collection of child nodes  * @param id  Parent node id * @param allMenu  All menu lists  * @return java.util.List<com.mozheng.manageframe.entity.MenuTest> * @author yizhixiansheng * @create 2021/6/30 **/
    private List<MenuTest> getChildList(Long id, List<MenuTest> allMenu) {
    
        //  Get all the child nodes under the passed node 
        List<MenuTest> childList = allMenu
                .stream()
                .filter(menuTest ->  menuTest.getPId().equals(id))
                .collect(Collectors.toList());
        //  When there is no child node under the transmitted node , Then exit recursion 
        if (Objects.isNull(childList) || childList.size() <= 0) {
    
            return new ArrayList<>();
        }
        //  Continue to recursive 
        childList.forEach(menuTest -> menuTest.setChildren(getChildList(menuTest.getId(), allMenu)));
        //  Sort according to the order field 
        childList.sort(Comparator.comparing(MenuTest::getSort));
        return childList;
    }

}

7. Create test class

package com.mozheng.manageframe;

import com.alibaba.fastjson.JSONObject;
import com.mozheng.manageframe.entity.Menu;
import com.mozheng.manageframe.entity.MenuTest;
import com.mozheng.manageframe.service.MenuService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.List;

@SpringBootTest
class ManageframeApplicationTests {
    

    @Autowired
    private MenuService menuService;

    @Test
    void contextLoads() {
    
        List<MenuTest> menuTestList = menuService.listInfo();
        System.out.println(JSONObject.toJSON(menuTestList));
    }

}

Look at the results

[{
    "children":[{
    "children":[{
    "children":[{
    "children":[{
    "children":[],"name":" Shuxi Lake ","pId":12,"showStatus":1,"id":15,"sort":3}],"name":" High-tech zone ","pId":8,"showStatus":1,"id":12,"sort":3}],"name":" Hefei ","pId":4,"showStatus":1,"id":8,"sort":1},{
    "children":[{
    "children":[{
    "children":[],"name":" Sungang town ","pId":10,"showStatus":1,"id":13,"sort":1},{
    "children":[],"name":" Chunshu town ","pId":10,"showStatus":1,"id":14,"sort":2}],"name":" Jin'an District ","pId":9,"showStatus":1,"id":10,"sort":1},{
    "children":[],"name":" Yu'an District ","pId":9,"showStatus":1,"id":11,"sort":2}],"name":" Lu'an City ","pId":4,"showStatus":1,"id":9,"sort":2}],"name":" Anhui Province ","pId":1,"showStatus":1,"id":4,"sort":1},{
    "children":[{
    "children":[],"name":" Xuzhou City ","pId":5,"showStatus":1,"id":7,"sort":1}],"name":" Jiangsu Province ","pId":1,"showStatus":1,"id":5,"sort":2},{
    "children":[{
    "children":[{
    "children":[{
    "children":[],"name":" Lingyin Temple ","pId":17,"showStatus":1,"id":18,"sort":1}],"name":" lake ","pId":16,"showStatus":1,"id":17,"sort":1}],"name":" hangzhou ","pId":6,"showStatus":1,"id":16,"sort":1}],"name":" Zhejiang Province ","pId":1,"showStatus":1,"id":6,"sort":3}],"name":" China ","pId":0,"showStatus":1,"id":1,"sort":1},{
    "children":[],"name":" The United States ","pId":0,"showStatus":1,"id":2,"sort":2},{
    "children":[],"name":" Canada ","pId":0,"showStatus":1,"id":3,"sort":3}]