Java递归如何实现菜单树

pom文件

    4.0.0
    
        org.springframework.boot
        spring-boot-starter-parent
        
        2.1.3.RELEASE
         
    
    com.example
    demo
    0.0.1-SNAPSHOT
    demo
    Demo project for Spring Boot
    
        1.8
    
    
        
            org.springframework.boot
            spring-boot-starter
        
        
            org.springframework.boot
            spring-boot-starter-web
        
        
            org.springframework.boot
            spring-boot-starter-thymeleaf
        
        
            org.springframework.boot
            spring-boot-starter-test
            test
        
        
        
            org.mybatis.spring.boot
            mybatis-spring-boot-starter
            2.1.1
        
        
        
            mysql
            mysql-connector-java
            runtime
        
        
        
            com.github.pagehelper
            pagehelper-spring-boot-starter
            1.3.0
        
        
        
            org.projectlombok
            lombok
            true
        
        
        
            com.baomidou
            mybatis-plus-boot-starter
            3.4.2
        
    
    
        
            
                org.springframework.boot
                spring-boot-maven-plugin
            
        
    

 application.yaml文件

spring:
  datasource:   
    url: jdbc:mysql://localhost:3306/springboot?useUnicode=true&characterEncoding=utf-8&serverTimezone=CTT
    username: root
    password: 2020
    driver-class-name: com.mysql.cj.jdbc.Driver
pagehelper:
  helperDialect: mysql
  reasonable: true # 修改默认值
# mybatis-plus配置
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  typeAliasesPackage: com.qcby.entity
  mapperLocations: classpath:mapper/*.xml
  # 全局配置id自增  =>
  global-config:
    db-config:
      id-type: auto

数据库表设计如下

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for menu
-- ----------------------------
DROP TABLE IF EXISTS `menu`;
CREATE TABLE `menu`  (
  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键id',
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin DEFAULT NULL COMMENT '名称',
  `pid` bigint(20) DEFAULT NULL COMMENT '父级id',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 10 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin ROW_FORMAT = Compact;
-- ----------------------------
-- Records of menu
-- ----------------------------
INSERT INTO `menu` VALUES (1, '主菜单1', 0);
INSERT INTO `menu` VALUES (2, '主菜单2', 0);
INSERT INTO `menu` VALUES (3, '主菜单3', 0);
INSERT INTO `menu` VALUES (4, '菜单1.1', 1);
INSERT INTO `menu` VALUES (5, '菜单1.2', 1);
INSERT INTO `menu` VALUES (6, '菜单1.1.1', 4);
INSERT INTO `menu` VALUES (7, '菜单2.1', 2);
INSERT INTO `menu` VALUES (8, '菜单2.2', 2);
INSERT INTO `menu` VALUES (9, '菜单1.1.2', 4);
SET FOREIGN_KEY_CHECKS = 1;

菜单类

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package com.qcby.entity;
import lombok.Data;
import java.util.List;
@Data//lombok实现简化 get、set、tostring方法
public class Menu {
    // 菜单id
    private String  id;
    //菜单名称
    private String name;
    // 父菜单id
    private String pid;
    // 子菜单
    private List menuChildren;
}

xml文件

    
        SELECT * FROM menu WHERE  pid=#{pid}
    
    
        SELECT * FROM menu
    
    
        SELECT * FROM menu where pid!= 0
    

Mapper层

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package com.qcby.mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.qcby.entity.Menu;
import org.apache.ibatis.annotations.Mapper;
import java.util.List;
@Mapper
public interface MenuMapper extends BaseMapper {
    List selectByPid(Integer pid);
    List selectAll();
    List selectAllNotBase();
}

service层

package com.qcby.service;
import com.baomidou.mybatisplus.extension.service.IService;
import com.qcby.entity.Menu;
import java.util.List;
public interface MenuService extends IService {
    List selectByPid(Integer pid);
    List selectAll();
    List selectAllNotBase();
}

serviceImpl

package com.qcby.service.Impl;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.qcby.entity.Menu;
import com.qcby.mapper.MenuMapper;
import com.qcby.service.MenuService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
@Service
public class MenuServiceImpl extends ServiceImpl implements MenuService {
    @Autowired
    private MenuMapper menuMapper;
    @Override
    public List selectByPid(Integer pid) {
        return menuMapper.selectByPid(pid);
    }
    @Override
    public List selectAll() {
        return menuMapper.selectAll();
    }
    @Override
    public List selectAllNotBase() {
        return menuMapper.selectAllNotBase();
    }
}

controller层

package com.qcby.controller;
import com.baomidou.mybatisplus.core.toolkit.StringUtils;
import com.qcby.entity.Menu;
import com.qcby.mapper.MenuMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.ArrayList;
import java.util.List;
@RestController
@RequestMapping("menu")
public class MenuController {
    @Autowired
    private MenuMapper menuMapper;
    @RequestMapping("/getMenuTree")
    public List getMenuTree(){
        List menusBase = menuMapper.selectByPid(0);
        List menuLNotBase = menuMapper.selectAllNotBase();
        for (Menu menu : menusBase) {
            List menus = iterateMenus(menuLNotBase, menu.getId());
            menu.setMenuChildren(menus);
        }
        return  menusBase;
    }
    /**
     *多级菜单查询方法
     * @param menuVoList 不包含最高层次菜单的菜单集合
     * @param pid 父类id
     * @return
     */
    public List iterateMenus(List menuVoList,String pid){
        List result = new ArrayList();
        for (Menu menu : menuVoList) {
            //获取菜单的id
            String menuid = menu.getId();
            //获取菜单的父id
            String parentid = menu.getPid();
            if(StringUtils.isNotBlank(parentid)){
                if(parentid.equals(pid)){
                    //递归查询当前子菜单的子菜单
                    List iterateMenu = iterateMenus(menuVoList,menuid);
                    menu.setMenuChildren(iterateMenu);
                    result.add(menu);
                }
            }
        }
        return result;
    }
}

结果展示