Java递归应用：输出树形菜单

树节点类：

package cn.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 cn.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;
}
}

测试类：

package zzj.test;

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：

<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：