java 递归菜单树（详细）

1.表结构

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for menu
-- ----------------------------
DROP TABLE IF EXISTS `menu`;
CREATE TABLE `menu` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `menu_name` varchar(64) NOT NULL COMMENT '菜单名称',
  `order_num` int(11) DEFAULT NULL COMMENT '菜单顺序',
  `url` varchar(64) DEFAULT NULL COMMENT '菜单路径',
  `pid` varchar(11) DEFAULT NULL COMMENT '上级Id',
  `icon` varchar(255) DEFAULT NULL COMMENT '菜单图标',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of menu
-- ----------------------------
INSERT INTO `menu` VALUES ('1', '系统管理', '1', '', '0', null);
INSERT INTO `menu` VALUES ('2', '轨迹查询', '2', '', '0', null);
INSERT INTO `menu` VALUES ('3', '设备信息', '3', '', '0', null);
INSERT INTO `menu` VALUES ('4', '用户信息', '1', '', '1', null);
INSERT INTO `menu` VALUES ('5', '客户信息', '2', null, '1', null);
INSERT INTO `menu` VALUES ('6', '用户资料', '1', null, '4', null);
INSERT INTO `menu` VALUES ('7', '客户资料', '1', null, '5', null);
INSERT INTO `menu` VALUES ('8', '切割机', '1', null, '3', null);
INSERT INTO `menu` VALUES ('9', '铲车', '2', null, '3', null);
INSERT INTO `menu` VALUES ('10', '割片', '1', null, '8', null);

2.菜单实体类

import lombok.Data;
import java.io.Serializable;
import java.util.List;
import javax.persistence.*;


/**
 *
 * @author m
 * @email 123456789@qq.com
 * @date 2019-12-13 16:54:59
 */
@Data
@Table(name = "menu")
public class Menu implements Serializable {
	private static final long serialVersionUID = 1L;
	
	//
    @Id
    private Integer id;
	
    //菜单名称
    @Column(name = "menu_name")
    private String menuName;
	
    //菜单顺序
    @Column(name = "order_num")
    private Integer orderNum;
	
    //菜单路径
    @Column(name = "url")
    private String url;
	
    //上级Id
    @Column(name = "pid")
    private String pid;
	
    //菜单图标
    @Column(name = "icon")
    private String icon;

	//子菜单
	@Transient
	private List<Menu> children;


}

3.菜单树

 /**
     * 获取菜单树
     * @return
     */
    public List<Menu> menuTree() {
        //查询所有菜单
        List<Menu> menus = mapper.selectAll();
        //返回的菜单树
        List<Menu> rootMenus = new ArrayList<>();
        for (Menu menu : menus) {
            //pid（上级Id）为0的是根菜单
            if ("0".equals(menu.getPid())) {
                rootMenus.add(menu);
            }
        }
        //遍历，找到二级菜单（根菜单的id和所有菜单中的pid比较）
        for (Menu rootMenu : rootMenus) {
            List<Menu> child = getChild(String.valueOf(rootMenu.getId()), menus);
            rootMenu.setChildren(child);
        }
        return rootMenus;
    }


    /**
     * 递归获取下级菜单
     * @param pid  上级Id
     * @param menus  所有菜单
     * @return
     */
    public List<Menu> getChild(String pid, List<Menu> menus) {
        //子菜单列表
        List<Menu> childList = new ArrayList<>();
        for (Menu menu : menus) {
            if (pid.equals(menu.getPid())) {
                childList.add(menu);
            }
        }
        //遍历 获取子菜单的子菜单
        for (Menu menu : childList) {
            List<Menu> child = getChild(String.valueOf(menu.getId()), menus);
            menu.setChildren(child);
        }
        //递归出口  childList长度为0
        if (childList.size() == 0) {
            return new ArrayList<>();
        }
        return childList;
    }

4.测试

{
    "status": 200,
    "message": "操作成功",
    "data": [
        {
            "id": 1,
            "menuName": "系统管理",
            "orderNum": 1,
            "url": "",
            "pid": "0",
            "icon": null,
            "children": [
                {
                    "id": 4,
                    "menuName": "用户信息",
                    "orderNum": 1,
                    "url": "",
                    "pid": "1",
                    "icon": null,
                    "children": [
                        {
                            "id": 6,
                            "menuName": "用户资料",
                            "orderNum": 1,
                            "url": null,
                            "pid": "4",
                            "icon": null,
                            "children": []
                        }
                    ]
                },
                {
                    "id": 5,
                    "menuName": "客户信息",
                    "orderNum": 2,
                    "url": null,
                    "pid": "1",
                    "icon": null,
                    "children": [
                        {
                            "id": 7,
                            "menuName": "客户资料",
                            "orderNum": 1,
                            "url": null,
                            "pid": "5",
                            "icon": null,
                            "children": []
                        }
                    ]
                }
            ]
        },
        {
            "id": 2,
            "menuName": "轨迹查询",
            "orderNum": 2,
            "url": "",
            "pid": "0",
            "icon": null,
            "children": []
        },
        {
            "id": 3,
            "menuName": "设备信息",
            "orderNum": 3,
            "url": "",
            "pid": "0",
            "icon": null,
            "children": [
                {
                    "id": 8,
                    "menuName": "切割机",
                    "orderNum": 1,
                    "url": null,
                    "pid": "3",
                    "icon": null,
                    "children": [
                        {
                            "id": 10,
                            "menuName": "割片",
                            "orderNum": 1,
                            "url": null,
                            "pid": "8",
                            "icon": null,
                            "children": []
                        }
                    ]
                },
                {
                    "id": 9,
                    "menuName": "铲车",
                    "orderNum": 2,
                    "url": null,
                    "pid": "3",
                    "icon": null,
                    "children": []
                }
            ]
        }
    ]
}

5.菜单树工具类

菜单树工具类