Java 递归实现树形菜单

1、实现效果：

2、实现思路：

递归生成思路，编写两个类: 数据模型Menu、和 创建树形的MenuTree。通过以下过程实现：

1.首先从菜单数据中获取所有根节点。
2.为根节点建立次级子树并拼接上。
3.递归为子节点建立次级子树并接上，直至为末端节点拼接上空的“树”。

3、实现代码

1、首先，编写数据模型Menu。每条菜单有自己的menuId、父节点parentId、菜单名称menuDescribe、菜单还拥有次级菜单children。

 * @Author dw
 * @ClassName Menu
 * @Description
 * @Date 2021/11/30 17:35
 * @Version 1.0
 */
@Data
public class Menu {
    private String menuId;
    private String parentId;
    private String menuDescribe;
    private String url;
    private List children;

    public Menu(String menuId, String parentId, String menuDescribe, String url) {
        this.menuId = menuId;
        this.parentId = parentId;
        this.menuDescribe = menuDescribe;
        this.url = url;
    }
    
}

2、创建树形结构的类MenuTree。方法getRootNode获取所有根节点，方法buildTree将根节点汇总创建树形结构，buildChildTree为节点建立次级树并拼接上当前树，递归调用buildChildTree不断为当前树开枝散叶直至找不到新的子树。完成递归，获取树形结构。

public class MenuTree {

    
    private List menuList = new ArrayList();

    public MenuTree(List menuList) {
        this.menuList = menuList;
    }

    
    public List buildTree() {
        List treeMenus = new ArrayList();
        for (Menu menuNode : getRootNode()) {
            menuNode = buildChildTree(menuNode);
            treeMenus.add(menuNode);
        }
        return treeMenus;
    }

    
    private Menu buildChildTree(Menu pNode) {
        List childMenus = new ArrayList();
        for (Menu menuNode : menuList) {
            if (menuNode.getParentId().equals(pNode.getMenuId())) {
                childMenus.add(buildChildTree(menuNode));
            }
        }
        pNode.setChildren(childMenus);
        return pNode;
    }

    
    private List getRootNode() {
        List rootMenuLists = new ArrayList();
        for (Menu menuNode : menuList) {
            if (menuNode.getParentId().equals("0")) {
                rootMenuLists.add(menuNode);
            }
        }
        return rootMenuLists;
    }
}

3、最后，插入一些数据试试效果。得到的json就可以生成图一菜单了。

public static void main(String[] args) {
        List menuList= new ArrayList();
        
        menuList.add(new Menu("GN001D000","0","系统管理","/admin"));
        menuList.add(new Menu("GN001D100","GN001D000","权限管理","/admin"));
        menuList.add(new Menu("GN001D110","GN001D100","密码修改","/admin"));
        menuList.add(new Menu("GN001D120","GN001D100","新加用户","/admin"));
        menuList.add(new Menu("GN001D200","GN001D000","系统监控","/admin"));
        menuList.add(new Menu("GN001D210","GN001D200","在线用户","/admin"));
        menuList.add(new Menu("GN002D000","0","订阅区","/admin"));
        menuList.add(new Menu("GN003D000","0","未知领域","/admin"));
        
        MenuTree menuTree =new MenuTree(menuList);
        menuList=menuTree.buildTree();
        
        String jsonOutput = JSONUtil.toJsonStr(menuList);
        System.out.println(jsonOutput);
    }

4、测试结果：

[{
    "parentId": "0",
    "url": "/admin",
    "menuDescribe": "系统管理",
    "children": [{
        "parentId": "GN001D000",
        "url": "/admin",
        "menuDescribe": "权限管理",
        "children": [{
            "parentId": "GN001D100",
            "url": "/admin",
            "menuDescribe": "密码修改",
            "children": [],
            "menuId": "GN001D110"
        }, {
            "parentId": "GN001D100",
            "url": "/admin",
            "menuDescribe": "新加用户",
            "children": [],
            "menuId": "GN001D120"
        }],
        "menuId": "GN001D100"
    }, {
        "parentId": "GN001D000",
        "url": "/admin",
        "menuDescribe": "系统监控",
        "children": [{
            "parentId": "GN001D200",
            "url": "/admin",
            "menuDescribe": "在线用户",
            "children": [],
            "menuId": "GN001D210"
        }],
        "menuId": "GN001D200"
    }],
    "menuId": "GN001D000"
}, {
    "parentId": "0",
    "url": "/admin",
    "menuDescribe": "订阅区",
    "children": [],
    "menuId": "GN002D000"
}, {
    "parentId": "0",
    "url": "/admin",
    "menuDescribe": "未知领域",
    "children": [],
    "menuId": "GN003D000"
}]