php查找任何页面上的所有链接的方法

$html = file_get_contents('http://www.example.com');
$dom = new DOMDocument();
@$dom->loadHTML($html);
// grab all the on the page
$xpath = new DOMXPath($dom);
$hrefs = $xpath->evaluate("/html/body//a");
for ($i = 0; $i < $hrefs->length; $i++) {
$href = $hrefs->item($i);
$url = $href->getAttribute('href');
echo $url.'<br />';
}