短网址的原理解析

有人问我短网址到底怎么做，自己能做吗？我说可以而且原理非常简单？下边是我的代码和配置分享出来，叫你2分钟急速编程做短网址 win8的iis8的 URL rewrite 支持iis7

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <rewrite>
            <rules>
                <rule name="url">
                    <match url="^(.*)a(.*)$" />
                    <action type="Rewrite" url="{R:1}/index.php?a={R:2}" />
                </rule>
            </rules>
        </rewrite>
    </system.webServer>
</configuration>

[ISAPI_Rewrite]
# 3600 = 1 hour
CacheClockRate 3600
RepeatLimit 32
# Protect httpd.ini and httpd.parse.errors files
# from accessing through HTTP
RewriteRule ^(.*)a(.*)$ $1/index\.php\?a$2

# 将 RewriteEngine 模式打开
RewriteEngine On
# Rewrite 系统规则请勿修改
RewriteCond %{QUERY_STRING} ^(.*)$
RewriteRule ^a(.*)$ index.php?a=$1

<?php
/*
 *CREATE TABLE `url_demo` (
 *	  `id` int(11) NOT NULL AUTO_INCREMENT,
 *    `durl` varchar(9) NOT NULL,
 *	  `zurl` varchar(250) NOT NULL,
 *	  PRIMARY KEY (`id`)
 *	 ) ENGINE=MyISAM DEFAULT CHARSET=utf8;
 *
 */
	$conn = mysql_connect("localhost","root","");
	mysql_select_db("test",$conn);
	$u = $_GET[a];
	$sql = "select zurl from url_demo where durl = '".$u."'";
	$data = mysql_query($sql);
	$result = mysql_fetch_array($data);
	if($result['zurl']!==""){
		header("Location:{$result['zurl']}");
	}
	
	//生成随机函数
	function create_randomstr($lenth = 6) {
		return random($lenth, '123456789bcdefghijklmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ');
	}

	function random($length, $chars = '0123456789') {
		$hash = '';
		$max = strlen($chars) - 1;
		for($i = 0; $i < $length; $i++) {
			$hash .= $chars[mt_rand(0, $max)];
		}
		return $hash;
	}
	$durl = create_randomstr(6);
	$zurl = 'http://www.widuu.cn';
	
	$sr = mysql_query("insert into url_demo (durl,zurl) value ('{$durl}','{$zurl}')");
	if($sr){
		echo "您的短网址是http://localhost/a".$durl;
	}