java从数据库读取菜单，递归生成菜单树

参考：https://blog.****.net/frankcheng5143/article/details/52958486

返回json结果：

{
"code": 0,
"msg": "成功",
"data": [
{
"menu_id": 1,
"parent_id": 0,
"name": "系统管理",
"url": null,
"perms": null,
"type": 0,
"icon": "system",
"order_num": 0,
"parentName": null,
"open": null,
"childMenus": [
{
"menu_id": 2,
"parent_id": 1,
"name": "管理员列表",
"url": "sys/user",
"perms": null,
"type": 1,
"icon": "admin",
"order_num": 1,
"parentName": null,
"open": null,
"childMenus": null
},
{
"menu_id": 3,
"parent_id": 1,
"name": "角色管理",
"url": "sys/role",
"perms": null,
"type": 1,
"icon": "role",
"order_num": 2,
"parentName": null,
"open": null,
"childMenus": null
},
{
"menu_id": 4,
"parent_id": 1,
"name": "菜单管理",
"url": "sys/menu",
"perms": null,
"type": 1,
"icon": "menu",
"order_num": 3,
"parentName": null,
"open": null,
"childMenus": null
},
{
"menu_id": 5,
"parent_id": 1,
"name": "SQL监控",
"url": "http://localhost:8080/renren-fast/druid/sql.html",
"perms": null,
"type": 1,
"icon": "sql",
"order_num": 4,
"parentName": null,
"open": null,
"childMenus": null
},
{
"menu_id": 6,
"parent_id": 1,
"name": "定时任务",
"url": "job/schedule",
"perms": null,
"type": 1,
"icon": "job",
"order_num": 5,
"parentName": null,
"open": null,
"childMenus": null
}
]
},
{
"menu_id": 31,
"parent_id": 0,
"name": "产成品管理",
"url": null,
"perms": null,
"type": 0,
"icon": "zhedie",
"order_num": 0,
"parentName": null,
"open": null,
"childMenus": [
{
"menu_id": 32,
"parent_id": 31,
"name": "成品",
"url": "chanchengpin/tang",
"perms": null,
"type": 1,
"icon": null,
"order_num": 0,
"parentName": null,
"open": null,
"childMenus": null
}
]
},
{
"menu_id": 30,
"parent_id": 0,
"name": "文件上传",
"url": "oss/oss",
"perms": "sys:oss:all",
"type": 1,
"icon": "oss",
"order_num": 6,
"parentName": null,
"open": null,
"childMenus": null
}
]
}

1.菜单实体类：

/**
 * @description:菜单管理
 * @author: Administrator
 * @date: 2019-03-01 14:14
 */
@Data
@TableName("sys_menu")
public class SysMenu {
    /**
     * 菜单ID
     */
    private long menu_id;
    /**
     * 父菜单ID，一级菜单为0
     */
    private long parent_id;
    /**
     * 菜单名称
     */
    private String name;
    /**
     * 菜单URL
     */
    private String url;
    /**
     * 授权(多个用逗号分隔，如：user:list,user:create)
     */
    private String perms;
    /**
     * 类型     0：目录   1：菜单   2：按钮
     */
    private int type;
    /**
     * 菜单图标
     */
    private String icon;
    /**
     * 排序
     */
    private int order_num;
    /**
     * 父菜单名称
     */
    @TableField(exist=false)
    private String parentName;

    /**
     * ztree属性
     */
    @TableField(exist=false)
    private Boolean open;

    /**
     * 子菜单
     */
    @TableField(exist=false)
    private List<SysMenu> childMenus;

}

// 原始的数据
List<SysMenu> sysMenuList=sysMenuDao.queryMenuList(role_id);

// 最后的结果
List<SysMenu> newMenuList = new ArrayList<>();

// 先找到所有的一级菜单
for (int i = 0; i < sysMenuList.size(); i++){
    SysMenu sysMenu=sysMenuList.get(i);
    Long parent_id=sysMenu.getParent_id();
    // 如果是顶级菜单，没有父菜单
    if (parent_id==0){
        newMenuList.add(sysMenu);
    }
}

// 为一级菜单设置子菜单，getChild是递归调用的
for (SysMenu menu : newMenuList) {
    menu.setChildMenus(getChild(menu.getMenu_id(), sysMenuList));
}

//    递归查找子菜单
private List<SysMenu> getChild(long id, List<SysMenu> rootMenu) {
    // 子菜单
    List<SysMenu> childList = new ArrayList<>();
    for (SysMenu menu : rootMenu) {
        // 遍历所有节点，将父菜单id与传过来的id比较
        if (menu.getParent_id()==id) {
            childList.add(menu);
        }
    }
    // 把子菜单的子菜单再循环一遍
    for (SysMenu menu : childList) {
        // 没有url子菜单还有子菜单
        if (menu.getUrl()==null) {
            // 递归
            menu.setChildMenus(getChild(menu.getMenu_id(), rootMenu));
        }
    } // 递归退出条件
    if (childList.size() == 0) {
        return null;
    }
    return childList;

}

java从数据库读取菜单，递归生成菜单树

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