bbs树形打印（一）

前言：大家在bbs回帖时常常可以看到树形的回复形式。

dfs设计

(1) 为使得Connection仅打开一次，因此以conn作为其中一个递归参数，在递归全程不关闭conn;

（2）根据存入数据的树状结构，由root的id逐层往下走；每到一个结点递归扫描该结点的子结点;

（3）打印时进行字符串拼接，故引入第三个递归参数：“level”;

数据准备：

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, ‘蚂蚁大战大象‘, ‘蚂蚁大战大象‘, now(), 1);
insert into article values (null, 1, 1, ‘大象被打趴下了‘, ‘大象被打趴下了‘,now(), 1);
insert into article values (null, 2, 1, ‘蚂蚁也不好过‘,‘蚂蚁也不好过‘, now(), 0);
insert into article values (null, 2, 1, ‘瞎说‘, ‘瞎说‘, now(), 1);
insert into article values (null, 4, 1, ‘没有瞎说‘, ‘没有瞎说‘, now(), 0);
insert into article values (null, 1, 1, ‘怎么可能‘, ‘怎么可能‘, now(), 1);
insert into article values (null, 6, 1, ‘怎么没有可能‘, ‘怎么没有可能‘, now(), 0);
insert into article values (null, 6, 1, ‘可能性是很大的‘, ‘可能性是很大的‘, now(), 0);
insert into article values (null, 2, 1, ‘大象进医院了‘, ‘大象进医院了‘, now(), 1);
insert into article values (null, 9, 1, ‘护士是蚂蚁‘, ‘护士是蚂蚁‘, now(), 0);

java封装

package com.gdufe.bbs;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class TreeShow {

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

    public static Connection getConnection() {
        Connection conn = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql://localhost/bbs";
            conn = DriverManager.getConnection(url, "root", "1234");
        } catch (Exception e) {
            e.printStackTrace();
        }
        return conn;
    }

    public static void show() {
        try {
            Connection conn = TreeShow.getConnection();
            Statement st = conn.createStatement();
            String sql = "select * from article where pid=0";
            ResultSet rs = st.executeQuery(sql);
            while (rs.next()) {
                System.out.println(rs.getInt("id") + rs.getString("cont"));
                tree(conn, rs.getInt("id"), 0);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void tree(Connection conn, int id, int level) {
        Statement st = null;
        ResultSet rs = null;
        StringBuffer preStr = new StringBuffer("    ");

        for (int i = 0; i < level; i++) {
            preStr.append("    ");
        }
        String sql = "select * from article where pid=" + id;
        try {
            st = conn.createStatement();
            rs = st.executeQuery(sql);
            while (rs.next()) {
                System.out.println(preStr + "" + rs.getInt("id")
                        + rs.getString("cont"));
                if (rs.getInt("isleaf") != 0) {
                    tree(conn, rs.getInt("id"), level + 1);
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

（注：为了方便代码理解，故意省去rs,st,conn的close()操作）

输出结果

1蚂蚁大战大象
    2大象被打趴下了
        3蚂蚁也不好过
        4瞎说
            5没有瞎说
        9大象进医院了
            10护士是蚂蚁
    6怎么可能
        7怎么没有可能
        8可能性是很大的