【Java递归】如何输出树形菜单

首先我们要建立树节点的类：

package com.tree;  

public class Node {  
    private Integer id;  
    private Integer parentId;  
    private String name;  
    private String link;  

    public Integer getId() {  
        return id;  
    }  
    public void setId(Integer id) {  
        this.id = id;  
    }  
    public Integer getParentId() {  
        return parentId;  
    }  
    public void setParentId(Integer parentId) {  
        this.parentId = parentId;  
    }  
    public String getName() {  
        return name;  
    }  
    public void setName(String name) {  
        this.name = name;  
    }  
    public String getLink() {  
        return link;  
    }  
    public void setLink(String link) {  
        this.link = link;  
    }  
}  

输出树形菜单类：

package com.tree;  

import java.util.ArrayList;  
import java.util.List;  

public class Tree {  
    private StringBuffer html = new StringBuffer();  
    private List<Node> nodes;  

    public Tree(List<Node> nodes){  
        this.nodes = nodes;  
    }  

    public String buildTree(){  
        html.append("<ul>");  
        for (Node node : nodes) {  
            Integer id = node.getId();  
            if (node.getParentId() == null) {  
                html.append("\r\n<li id='" + id + "'>" + node.getName()+ "</li>");  
                build(node);  
            }  
        }  
        html.append("\r\n</ul>");  
        return html.toString();  
    }  

    private void build(Node node){  
        List<Node> children = getChildren(node);  
        if (!children.isEmpty()) {  
            html.append("\r\n<ul>");  
            for (Node child : children) {  
                Integer id = child.getId();  
                html.append("\r\n<li id='" + id + "'>" + child.getName()+ "</li>");  
                build(child);  
            }  
            html.append("\r\n</ul>");  
        }   
    }  

    private List<Node> getChildren(Node node){  
        List<Node> children = new ArrayList<Node>();  
        Integer id = node.getId();  
        for (Node child : nodes) {  
            if (id.equals(child.getParentId())) {  
                children.add(child);  
            }  
        }  
        return children;  
    }  
}  

然后我们来测试一下：

import java.util.ArrayList;  
import java.util.List;  

import cn.com.tree.Node;  
import cn.com.tree.Tree;  


public class Test {  

    /** 
     * @param args 
     */  
    public static void main(String[] args) {  
        List<Node> nodes = new ArrayList<Node>();  

        Node node1 = new Node();  
        node1.setId(1);  
        node1.setName("node1");  
        node1.setParentId(null);  
        node1.setLink(null);  
        nodes.add(node1);  

        Node node11 = new Node();  
        node11.setId(11);  
        node11.setName("node11");  
        node11.setParentId(1);  
        node11.setLink(null);  
        nodes.add(node11);  

        Node node111 = new Node();  
        node111.setId(111);  
        node111.setName("node111");  
        node111.setParentId(11);  
        node111.setLink(null);  
        nodes.add(node111);  

        Node node12 = new Node();  
        node12.setId(12);  
        node12.setName("node12");  
        node12.setParentId(1);  
        node12.setLink(null);  
        nodes.add(node12);  

        Node node2 = new Node();  
        node2.setId(2);  
        node2.setName("node2");  
        node2.setParentId(null);  
        node2.setLink(null);  
        nodes.add(node2);  

        Node node21 = new Node();  
        node21.setId(21);  
        node21.setName("node21");  
        node21.setParentId(2);  
        node21.setLink(null);  
        nodes.add(node21);  

        Node node3 = new Node();  
        node3.setId(3);  
        node3.setName("node3");  
        node3.setParentId(null);  
        node3.setLink(null);  
        nodes.add(node3);  

        Tree tree = new Tree(nodes);  
        System.out.println(tree.buildTree());  
    }  
}  

输出的结果：

<ul>
<li id='1'>node1</li>
<ul>
<li id='11'>node11</li>
<ul>
<li id='111'>node111</li>
</ul>
<li id='12'>node12</li>
</ul>
<li id='2'>node2</li>
<ul>
<li id='21'>node21</li>
</ul>
<li id='3'>node3</li>
</ul>

浏览器效果：