递归输出树形节点

1.脚本

CREATE TABLE `a` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(10) DEFAULT NULL,
`parentid` int(11) DEFAULT NULL,
`parentName` varchar(10) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

/*Data for the table `a` */

insert into `a`(`id`,`name`,`parentid`,`parentName`) values (1,'中国',0,NULL),(2,'四川',1,'中国'),(3,'北京',1,'中国'),(4,'成都',2,'四川'),(5,'朝阳区',3,'北京');

2.DBUtil.java

package tree;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class DBUtil {
 //取得数据库连接
 public static Connection getConnection() {
  Connection conn = null;
  try {
   Class.forName("com.mysql.jdbc.Driver");
  } catch (ClassNotFoundException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
   System.out.println("驱动程序没有找到" + e.getMessage());
  }
  try {
   conn = DriverManager.getConnection(
     "jdbc:mysql://localhost:3306/test", "root", "123");
  } catch (SQLException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
   System.out.println("获得连接出错!");
  }
  return conn;
 }
}

3.节点类

package tree;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Vector;
public class TreeNode {
	private int id;
	private String name;
	private int parentId;
	private String parentName;
	public TreeNode(int id) {
		this.id = id;
		if (!init()) {
			this.id = -1;
		}
	}
	// 初始化节点
	public boolean init() {
		String sql = "select * from a where id=" + getId();
		Connection conn = null;
		Statement st = null;
		ResultSet rs = null;
		boolean flag = false;
		try {
			conn = DBUtil.getConnection();
			st = conn.createStatement();
			rs = st.executeQuery(sql);
			if (rs.next()) {
				this.parentId = rs.getInt("parentid");
				this.name = rs.getString("name");
				this.parentName = rs.getString("parentname");
				flag = true;
			}
			rs.close();
			st.close();
			conn.close();
		} catch (SQLException e) {
			e.printStackTrace();
			return false;
		}
		return flag;
	}
	// 是否可以展开
	public boolean canExpand() {
		boolean flag = false;
		String sql = "select * from a where parentid=" + getId();
		Connection conn = null;
		Statement st = null;
		ResultSet rs = null;
		try {
			conn = DBUtil.getConnection();
			st = conn.createStatement();
			rs = st.executeQuery(sql);
			if (rs.next()) {
				flag = true;
			}
			rs.close();
			st.close();
			conn.close();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return flag;
	}
	// 取得子节点列表
	public TreeNode[] getChildren() {
		String sql = "select id from a where parentid=" + getId();
		Connection conn = null;
		Statement st = null;
		ResultSet rs = null;
		Vector vData = new Vector();
		TreeNode[] children = null;
		try {
			conn = DBUtil.getConnection();
			st = conn.createStatement();
			rs = st.executeQuery(sql);
			while (rs.next())
				vData.add("" + rs.getInt("id"));
			children = new TreeNode[vData.size()];
			for (int i = 0; i < vData.size(); i++) {
				int id = Integer.parseInt((String) vData.get(i));
				children[i] = new TreeNode(id);
			}
			rs.close();
			st.close();
			conn.close();
		} catch (SQLException e) {
			e.printStackTrace();
			return null;
		}
		return children;
	}
	// 递归生成xml格式的字符串
	public static String getXMLString(TreeNode treeNode) {
		StringBuffer content = new StringBuffer();
		//输出当前节点
		content.append("<node label=/"" + treeNode.getName() + "/">");
		//如果有子节点的话，递归输出子节点的内容
		if (treeNode.canExpand()) {
			TreeNode[] elmts = treeNode.getChildren();
			for (int i = 0; i < elmts.length; i++)
				content.append(getXMLString(elmts[i]));
		}
		content.append("</node>");
		return content.toString();
	}
    //测试
	public static void main(String[] args) {
		TreeNode treeNode = new TreeNode(1);//根节点
		String result=getXMLString(treeNode);
		System.out.println(result);
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getParentId() {
		return parentId;
	}
	public void setParentId(int parentId) {
		this.parentId = parentId;
	}
	public String getParentName() {
		return parentName;
	}
	public void setParentName(String parentName) {
		this.parentName = parentName;
	}
	public void setId(int id) {
		this.id = id;
	}
	public int getId() {
		return id;
	}
}