DOMDocument::loadHTML()

(PHP 5, PHP 7)

Load HTML from a string

说明

publicDOMDocument::loadHTML(string $source[,int $options= 0]): bool

The function parses the HTML contained in the string$source. Unlike loading XML, HTML does not have to be well-formed to load. This function may also be called statically to load and create a DOMDocument object. The static invocation may be used when no DOMDocument properties need to be set prior to loading.

参数

$source: The HTML string.
$options: Since PHP 5.4.0 and Libxml 2.6.0, you may also use the$optionsparameter to specify additional Libxml parameters.

返回值

成功时返回TRUE，或者在失败时返回FALSE。 If called statically, returns a DOMDocument或者在失败时返回FALSE.

错误／异常

If an empty string is passed as the$source, a warning will be generated. This warning is not generated by libxml and cannot be handled using libxml's error handling functions.

此方法可以被静态调用,但会抛出一个E_STRICT错误。

尽管非正确格式化的 HTML 仍应该被成功调入，但此函数会在遇到错误标记时产生E_WARNING错误。libxml 错误处理函数可以用来处理这类错误。

范例

Example #1 Creating a Document

<?php
$doc = new DOMDocument();
$doc->loadHTML("<html><body>Test<br></body></html>");
echo $doc->saveHTML();
?>

更新日志

版本	说明
5.4.0	Added`$options`parameter.

参见

DOMDocument::loadHTMLFile() Load HTML from a file
DOMDocument::saveHTML() Dumps the internal document into a string using HTML formatting
DOMDocument::saveHTMLFile() Dumps the internal document into a file using HTML formatting

You can also load HTML as UTF-8 using this simple hack:
<?php
$doc = new DOMDocument();
$doc->loadHTML('<?xml encoding="UTF-8">' . $html);
// dirty fix
foreach ($doc->childNodes as $item)
  if ($item->nodeType == XML_PI_NODE)
    $doc->removeChild($item); // remove hack
$doc->encoding = 'UTF-8'; // insert proper
?>

DOMDocument is very good at dealing with imperfect markup, but it throws warnings all over the place when it does. 
This isn't well documented here. The solution to this is to implement a separate aparatus for dealing with just these errors. 
Set libxml_use_internal_errors(true) before calling loadHTML. This will prevent errors from bubbling up to your default error handler. And you can then get at them (if you desire) using other libxml error functions. 
You can find more info here http://www.php.net/manual/en/ref.libxml.php

When using loadHTML() to process UTF-8 pages, you may meet the problem that the output of dom functions are not like the input. For example, if you want to get "Cạnh tranh", you will receive "Cáº¡nh tranh". I suggest we use mb_convert_encoding before load UTF-8 page :
<?php
  $pageDom = new DomDocument();  
  $searchPage = mb_convert_encoding($htmlUTF8Page, 'HTML-ENTITIES', "UTF-8"); 
  @$pageDom->loadHTML($searchPage);
?>

Pay attention when loading html that has a different charset than iso-8859-1. Since this method does not actively try to figure out what the html you are trying to load is encoded in (like most browsers do), you have to specify it in the html head. If, for instance, your html is in utf-8, make sure you have a meta tag in the html's head section:
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
</head>
If you do not specify the charset like this, all high-ascii bytes will be html-encoded. It is not enough to set the dom document you are loading the html in to UTF-8.

Warning: This does not function well with HTML5 elements such as SVG. Most of the advice on the Web is to turn off errors in order to have it work with HTML5.

For those of you who want to get an external URL's class element, I have 2 usefull functions. In this example we get the '<h3 class="r">'
 elements back (search result headers) from google search:
1. Check the URL (if it is reachable, existing)
<?php
# URL Check
function url_check($url) { 
  $headers = @get_headers($url); 
  return is_array($headers) ? preg_match('/^HTTP\\/\\d+\\.\\d+\\s+2\\d\\d\\s+.*$/',$headers[0]) : false; 
};
?>
2. Clean the element you want to get (remove all tags, tabs, new-lines etc.)
<?php
# Function to clean a string
function clean($text){
  $clean = html_entity_decode(trim(str_replace(';','-',preg_replace('/\s+/S', " ", strip_tags($text)))));// remove everything
  return $clean;
  echo '\n';// throw a new line
}
?>
After doing that, we can output the search result headers with following method:
<?php
$searchstring = 'djceejay';
$url = 'http://www.google.de/webhp#q='.$searchstring;
if(url_check($url)){
  $doc = new DomDocument;
  $doc->validateOnParse = true;
  $doc->loadHtml(file_get_contents($url));
  $output = clean($doc->getElementByClass('r')->textContent);
  echo $output . '<br>';
}else{
  echo 'URL not reachable!';// Throw message when URL not be called
}
?>

It should be noted that when any text is provided within the body tag
outside of a containing element, the DOMDocument will encapsulate that
text into a paragraph tag (<p>).
For example:
<?php
$doc = new DOMDocument();
$doc->loadHTML("<html><body>Test<br><div>Text</div></body></html>");
echo $doc->saveHTML();
?>
will yield:
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html><body>
<p>Test<br></p>
<div>Text</div>
</body></html>
while:
<?php
$doc = new DOMDocument();
$doc->loadHTML(
  "<html><body><i>Test</i><br><div>Text</div></body></html>");
echo $doc->saveHTML();
?>
will yield:
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html><body>
<i>Test</i><br><div>Text</div>
</body></html>

Be aware that this function doesn't actually understand HTML -- it fixes tag-soup input using the general rules of SGML, so it creates well-formed markup, but has no idea which element contexts are allowed.
For example, with input like this where the first element isn't closed: 
  <span>hello <div>world</div>
loadHTML will change it to this, which is well-formed but invalid:
  <span>hello <div>world</div></span>

Remember: If you use an HTML5 doctype and a meta element like so
<meta charset=utf-8">
your HTML code will get interpreted as ISO-8859-something and non-ASCII chars will get converted into HTML entities. However the HTML4-like version will work (as has been pointed out 10 years ago by "bigtree at 29a"):
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

Note that the elements of such document will have no namespace even with <html xmlns="http://www.w3.org/1999/xhtml">

If you use loadHTML() to process utf HTML string (eg in Vietnamese), you may experience result in garbage text, while some files were OK. Even your HTML already have meta charset like
 <meta http-equiv="content-type" content="text/html; charset=utf-8">
I have discovered that, to help loadHTML() process utf file correctly, the meta tag should come first, before any utf string appear. For example, this HTML file
<html>
 <head>
  <meta http-equiv="content-type" content="text/html; charset=utf-8">
  <title> Vietnamese - Tiếng Việt</title>
 </head>
<body></body>
</html>
will be OK with loadHTML() when <meta> tag appear <title> tag.
But the file below will not regcornize by loadHTML() because <title> tag contains utf string appear before <meta> tag.
<html>
 <head>
  <title> Vietnamese - Tiếng Việt</title>
  <meta http-equiv="content-type" content="text/html; charset=utf-8">
 </head>
<body></body>
</html>

Using loadHTML() automagically sets the doctype property of your DOMDocument instance(to the doctype in the html, or defaults to 4.0 Transitional). If you set the doctype with DOMImplementation it will be overridden.
I assumed it was possible to set it and then load html with the doctype I defined(in order to decide the doctype at runtime), and ran into a huge headache trying to find out where my doctype was going. Hopefully this helps someone else.

Here is a function I wrote to capitalize the previous remarks about charset problems (UTF-8...) when using loadHTML and then DOM functions.
It adds the charset meta tag just after <head> to improve automatic encoding detection, converts any specific character to an html entity, thus PHP DOM functions/attributes will return correct values.
<?php
mb_detect_order("ASCII,UTF-8,ISO-8859-1,windows-1252,iso-8859-15");
function loadNprepare($url,$encod='') {
    $content    = file_get_contents($url);
    if (!empty($content)) {
        if (empty($encod))
            $encod = mb_detect_encoding($content);
        $headpos    = mb_strpos($content,'<head>');
        if (FALSE=== $headpos)
            $headpos= mb_strpos($content,'<HEAD>');
        if (FALSE!== $headpos) {
            $headpos+=6;
            $content = mb_substr($content,0,$headpos) . '<meta http-equiv="Content-Type" content="text/html; charset='.$encod.'">' .mb_substr($content,$headpos);
        }
        $content=mb_convert_encoding($content, 'HTML-ENTITIES', $encod);
    }
    $dom = new DomDocument;
    $res = $dom->loadHTML($content);
    if (!$res) return FALSE;
    return $dom;
}
?>
NB: it uses mb_strpos/mb_substr instead of mb_ereg_replace because that seemed more efficient with huge html pages.

Beware of the "gotcha" (works as designed but not as expected): if you use loadHTML, you cannot validate the document. Validation is only for XML. Details here: http://bugs.php.net/bug.php?id=43771&edit=1