RecursiveDOMIterator
PHP provides several extensions to work with XML. One of them is DOM, which is an implementation of the W3C DOM Interface. While quite powerful, DOM lacks the capability to iterate over the entire DOM tree at once. To get around this limitation, we can create a custom class that implements SPL's RecursiveIterator interface to allow us to easily and fully traverse the DOM tree with foreach.
Internally, DOM uses the DOMNodeList class to collect and provide access to children of a DOMNode. The RecursiveDOMIterator will aggregate the DOMNodeList referenced in a DOMNode::childNodes property. When iterating over the DOMNodeList, the iterator has to keep track of the current position internally. The remaining work is implementing the methods demanded by the RecursiveIterator interface then.
<?php
class RecursiveDOMIterator implements RecursiveIterator
{
/**
* Current Position in DOMNodeList
* @var Integer
*/
protected $_position;
/**
* The DOMNodeList with all children to iterate over
* @var DOMNodeList
*/
protected $_nodeList;
/**
* @param DOMNode $domNode
* @return void
*/
public function __construct(DOMNode $domNode)
{
$this->_position = 0;
$this->_nodeList = $domNode->childNodes;
}
/**
* Returns the current DOMNode
* @return DOMNode
*/
public function current()
{
return $this->_nodeList->item($this->_position);
}
/**
* Returns an iterator for the current iterator entry
* @return RecursiveDOMIterator
*/
public function getChildren()
{
return new self($this->current());
}
/**
* Returns if an iterator can be created fot the current entry.
* @return Boolean
*/
public function hasChildren()
{
return $this->current()->hasChildNodes();
}
/**
* Returns the current position
* @return Integer
*/
public function key()
{
return $this->_position;
}
/**
* Moves the current position to the next element.
* @return void
*/
public function next()
{
$this->_position++;
}
/**
* Rewind the Iterator to the first element
* @return void
*/
public function rewind()
{
$this->_position = 0;
}
/**
* Checks if current position is valid
* @return Boolean
*/
public function valid()
{
return $this->_position < $this->_nodeList->length;
}
}Like any other RecursiveIterator, the RecursiveDOMIterator has to be wrapped into a RecursiveIteratorIterator to go over children recursively. The example below would load the contents of a book.xml file into a DOMDocument, wrap it's instance into the appropriate iterators and then output all element nodes. Of course, this could be combined with additional iterators, like FilterIterator.
<?php
$dom = new DOMDocument; // create new DOMDocument instance
$dom->load('books.xml'); // load DOMDocument with XML data
$dit = new RecursiveIteratorIterator(
new RecursiveDOMIterator($dom),
RecursiveIteratorIterator::SELF_FIRST);
foreach($dit as $node) {
if($node->nodeType === XML_ELEMENT_NODE) {
echo $node->nodeName, PHP_EOL;
}
}