php获取重定向后的URL地址的实例代码

在php中，经常使用.htaccess实现url的重定向，不过，有时又需要获取重定向后的页面地址。
本文给出的例子，可以取得重定向后的url地址，如下：

<?php
//取重定向的地址 
class RedirectUrl{ 
//地址 
var $url; 
//初始化地址 
function RedirectUrl($url){ 
$this->url = $url; 
} 
/** 
* get_redirect_url() 
* 取重定向的地址 
* //by www.jb200.com
* @param string $url 
* @return string 
*/ 
private function get_redirect_url($url){ 
$redirect_url = null; 

$url_parts = @parse_url($url); 
if (!$url_parts) return false; 
if (!isset($url_parts['host'])) return false; //can't process relative URLs 
if (!isset($url_parts['path'])) $url_parts['path'] = '/'; 

$sock = fsockopen($url_parts['host'], (isset($url_parts['port']) ? (int)$url_parts['port'] : 80), $errno, $errstr, 30); 
if (!$sock) return false; 

$request = "HEAD " . $url_parts['path'] . (isset($url_parts['query']) ?'?'.$url_parts['query'] : '') . " HTTP/1.1rn"; 
$request .= 'Host: ' . $url_parts['host'] . "rn"; 
$request .= "Connection: Closernrn"; 
fwrite($sock, $request); 
$response = ''; 
while(!feof($sock)) $response .= fread($sock, 8192); 
fclose($sock); 

if (preg_match('/^Location: (.+?)$/m', $response, $matches)){ 
return trim($matches[1]); 
} else { 
return false; 
} 
} 

/** 
* get_all_redirects() 
* 取所有重定向地址 
* 
* @param string $url 
* @return array 
*/ 
private function get_all_redirects($url){ 
$redirects = array(); 
while ($newurl = $this->get_redirect_url($url)){ 
if (in_array($newurl, $redirects)){ 
break; 
} 
$redirects[] = $newurl; 
$url = $newurl; 
} 
return $redirects; 
} 

/** 
* get_final_url() 
* 取实际地址 
* 
* @param string $url 
* @return string 
*/ 
function get_final_url(){ 
$redirects = $this->get_all_redirects($this->url); 

if (count($redirects)>0){ 
return array_pop($redirects); 
} else { 
return $this->url; 
} 
} 
} 

/** 
* get_show_pic 
* 取最终要显示的图片地址 
* 
* @param string $url 
* @return string 
*/ 
function get_show_pic($url,$noimg ='noimg.gif',$newimg="http://www.jb200.com/images/slt-1.jpg"){ 
$obj = new RedirectUrl($url); 

$realurl = $obj->get_final_url(); 

if(strpos($realurl,$noimg)>0){ 
return $newimg; 
} 
return $url; 
} 
//参考 
echo "<img src='".get_show_pic("http://www.jb200.com/img/1294948410019/5.jpg")."'/>"; 
?>