php获取页面a里面的链接

获取网站里面a的链接，想到用个php函数实现，如何操作?

<?php
function sj($url){
$html = file_get_contents($url);

$dom = new DOMDocument();
@$dom->loadHTML($html);

$xpath = new DOMXPath($dom);
$hrefs = $xpath->evaluate('/html/body//a');

for ($i = 0; $i < $hrefs->length; $i++) {
$href = $hrefs->item($i);
$url = $href->getAttribute('href');


}
}
$url='http://www.henenseo.com/';

sj($url);

?>