Java递归实现树状结构

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只是简单实现树状结构，后续进行补充。

package com.tree.test;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;public class Test {public static void main(String[] args){showTree();}     public static void showTree(){       Connection conn=null;    ResultSet  rs = null;    Statement stmt=null;    try {Class.forName("com.mysql.jdbc.Driver");conn=DriverManager.getConnection("jdbc:mysql://localhost/tree?user=root&password=root");/*stmt=conn.createStatement();rs=stmt.executeQuery("select * from country where pid=0");while(rs.next()){System.out.println(rs.getString("actile"));*/tree(conn,0,0);   // }} catch (Exception e) {// TODO Auto-generated catch blocke.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();}}     }     public static void tree(Connection conn,int id,int level){    Statement stmt = null;    ResultSet rs = null;                try {    stmt = conn.createStatement();    String sql = "select * from country where pid = " + id;    rs = stmt.executeQuery(sql);    while(rs.next()) {    StringBuffer strPre = new StringBuffer("");        for(int i=0; i<level; i++) {        strPre.append("    ");        }    System.out.println(strPre + rs.getString("actile"));    if(rs.getInt("is_leaf") != 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();    }    }    }

数据库

create database tree;use tree;create table country (id int primary key auto_increment,pid int,actile varchar(40),is_leaf int );insert into country values(1,0, '中国',1);insert into country values(2,1,'北京',0);insert into country values(3,0,'美国',1);insert into country values(4,3,'纽约',0);insert into country values(5,1,'浙江',1);insert into country values(6,5,'杭州',1);insert into country values(7,6,'滨江',0);

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