樹狀列出數據庫內的文章練習

首先在mysql新建一個bbs的表，並且插入數據：

create database bbs;

use bbs;

create table article (
id int primary key auto_increment,
pid int,
rootid int,
title varchar(255),
cont text,
pdate datetime,
isleaf int
);

insert into article values (null,0,1,'螞蟻大戰大象','螞蟻大戰大象',now(),1);
insert into article values (null,1,1,'大象被打趴了','大象被打趴了',now(),1);
insert into article values (null,2,1,'螞蟻也不好過','螞蟻也不好過',now(),0);
insert into article values (null,2,1,'瞎說','瞎說',now(),1);
insert into article values (null,4,1,'沒有瞎說','沒有瞎說',now(),0);
insert into article values (null,1,1,'怎麼可能','怎麼可能',now(),1);
insert into article values (null,6,1,'怎麼沒有可能','怎麼沒有可能',now(),0);
insert into article values (null,6,1,'可能性很大','可能性很大',now(),0);
insert into article values (null,2,1,'大象進醫院了','大象進醫院了',now(),1);
insert into article values (null,9,1,'護士是螞蟻','護士是螞蟻',now(),0);



--輸出結果類似於
--螞蟻大戰大象
--    大象被打趴下了
--        螞蟻也不好過
--        瞎說
--            沒有瞎說
-- 大象進醫院了
--             護士是螞蟻
--    怎麼可能
--        怎麼沒有可能
--        可能性很大的

import java.sql.*;

public class ArticleTree {

	public static void main(String[] args) {
		new ArticleTree().show();
	}

	public void show() {
		Connection conn = null;
		Statement stmt = null;
		ResultSet rs = null;

		try {
			Class.forName("com.mysql.jdbc.Driver");
			conn = DriverManager
					.getConnection("jdbc:mysql://localhost/bbs?user=root&password=root");
			stmt = conn.createStatement();
			rs = stmt.executeQuery("select * from article where pid=0");
			while(rs.next()) {
				System.out.println(rs.getString("cont"));
				tree(conn, rs.getInt("id"), 1);
			}
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			try {
				if(rs != null) {
					rs.close();
					rs = null;
				}
				if(stmt != null) {
					stmt.close();
					stmt = null;
				}
				if(conn != null) {
					conn.close();
					conn = null;
				}
			} catch(SQLException e) {
				e.printStackTrace();
			}
		}
	}

	private void tree(Connection conn, int id, int level) {
		Statement stmt = null;
		ResultSet rs = null;

		StringBuffer strPre = new StringBuffer();
		for (int i = 0; i < level; i++) {
			strPre.append("    ");
		}

		try {
			stmt = conn.createStatement();
			String sql = "select * from article where pid=" + id;
			rs = stmt.executeQuery(sql);
			while (rs.next()) {
				System.out.println(strPre + rs.getString("cont"));
				if (rs.getInt("isleaf") != 0) {
					tree(conn, rs.getInt("id"), level + 1);
				}
			}
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			try {
				if (rs != null) {
					rs.close();
					rs = null;
				}
				if (stmt != null) {
					stmt.close();
					stmt = null;
				}
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
}