PHP parsing html class library simple_html_dom (detailed introduction)

Download address: https://github.com/samacs/simple_html_dom

The parser not only helps us verify html documents; it can also parse html documents that do not comply with W3C standards. It uses an element selector similar to jQuery to find and locate elements by their id, class, tag, etc.; it also provides the functions of adding, deleting, and modifying the document tree. Of course, such a powerful html Dom parser is not perfect; you need to be very careful about memory consumption during use. However, don’t worry; in this article, I will explain how to avoid consuming too much memory at the end.
Start using
After uploading a class file, there are three ways to call this class:
Load html document from url
Load html document from string
Load html document from file

Copy code The code is as follows:

/ / Create a new Dom instance
$html = new simple_html_dom();

// Load from url
$html->load_file('http://www.jb51.net') ;

//Load from string
$html->load('Load html document demo from string
//Load from file
$html->load_file('path/file/test.html');
?>

If you load an html document from a string, you need to download it from the Internet first. It is recommended to use cURL to grab html documents and load them into the DOM.
Find html elements
You can use the find function to find elements in the html document. The returned result is an array containing objects. We use the functions in the HTML DOM parsing class to access these objects. Here are a few examples:

Copy the code The code is as follows:

 

//Find hyperlink elements in html documents
$a = $html->find('a');

//Find The (N)th hyperlink in the document, if not found, returns an empty array.
$a = $html->find('a', 0);

//The search id is main The div element 
$main = $html->find('div[id=main]',0);

// Find all div elements containing the id attribute 
$divs = $html->find('div[id]');

// Find all elements containing the id attribute
$divs = $html->find('[id]' );
?>

You can also use a jQuery-like selector to find positioned elements:

Copy code The code is as follows:

// Find the element with id='#container'
$ret = $html->find('#container');

// Find all elements with class=foo
$ret = $html->find('.foo');

// Find multiple html tags
$ ret = $html->find('a, img');

// You can also use it like this
$ret = $html->find('a[title], img[title ]');
?>

The parser supports searching for child elements

Copy code The code is as follows:

// Find all li items in the ul list
$ret = $html->find('ul li');

//Find the li item with class=selected specified in the ul list
$ret = $html->find('ul li.selected');

?>

If you find this troublesome, you can use built-in functions to easily locate the parent, child and adjacent elements of an element

Copy code The code is as follows:

// Returns the parent element
$e->parent;

// Returns the array of child elements
$ e->children;

// Return the specified child element by index number
$e->children(0);

// Return the first resource speed
$e->first_child ();

// Return the last child element
$e->last _child ();

// Return the previous adjacent element 
$e->prev_sibling ();

//Return the next adjacent element
$e->next_sibling ();
?>

Element Attribute Operations
Use simple regular expressions to operate attribute selectors.
[attribute] - selects html elements that contain a certain attribute
[attribute=value] - selects all html elements with a specified value attribute
[attribute!=value] - selects all html elements with a non-specified value attribute
[attribute^=value] - selects all html elements with attributes starting with a specified value
[attribute$=value] selects all html elements with attributes ending with a specified value
[attribute*=value] - selects all elements containing The html element
that specifies the value attribute calls the element attribute in the parser
. The element attribute in the DOM is also an object:

Copy the code The code is as follows:

// In this example, the anchor link value of $a is assigned to the $link variable
$link = $a->href;
?>

or:

Copy the code The code is as follows:

$ link = $html->find('a',0)->href;
?

Each object has 4 basic object properties:
tag – return html tag name
innertext - returns innerHTML
outertext - returns outerHTML
plaintext - returns the text in the html tag
Editing elements in the parser
The usage of editing element attributes is similar to calling them of:

Copy code The code is as follows:

//Assign the anchor link of $a New value
$a->href = 'http://www.jb51.net';

// Delete anchor link
$a->href = null;
 
//Detect whether there is an anchor link
if(isset($a->href)) {
//Code
}
?>

There is no special method to add or delete elements in the parser, but you can use it differently:

Copy the code The code is as follows:

// Encapsulation element
$e->outertext = '

' . $e->outertext . '

';

// Delete element
$e->outertext = '';

// Add element
$e->outertext = $e->outertext . '

foo

';

// Insert element
$e->outertext = '

foo

' . $e->outertext;
?

Saving the modified html DOM document is also very simple:

Copy the code The code is as follows:

$doc = $html;
// Output
echo $doc;
?>

How to avoid the parser consuming too much memory
At the beginning of this article, the author mentioned the problem of the Simple HTML DOM parser consuming too much memory. If the php script takes up too much memory, it will cause the website to stop responding and a series of serious problems. The solution is also very simple. After the parser loads the HTML document and uses it, remember to clean up this object. Of course, don't take the problem too seriously. If only 2 or 3 documents are loaded, cleaning or not cleaning does not make much difference. When you load 5, 10 or more documents, it is absolutely your responsibility to clear the memory after using one ^_^

Copy code The code is as follows:

$html->clear();
?>

Related labels：

dom html https php simple download introduce address Class library parse detailed

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