Parse XML with PHP and XMLReader

Question

I\'ve been trying to parse a very large XML file with PHP and XMLReader, but can\'t seem to get the results I am looking for. Basically, I\'m searching a ton of information

Answer 1

To gain more flexibility with XMLReader I normally create myself iterators that are able to work on the XMLReader object and provide the steps I need.

That starts with a simple iteration over all nodes over to the iteration over elements optionally with a specific name. Let's call the last one XMLElementIterator taking the reader and the element name as parameters.

In your scenario I then would create an iterator that returns a SimpleXMLElement for the current element, taking only the elements:

require('xmlreader-iterators.php'); // https://gist.github.com/hakre/5147685

class HeadendIterator extends XMLElementIterator {
    const ELEMENT_NAME = 'headend';

    public function __construct(XMLReader $reader) {
        parent::__construct($reader, self::ELEMENT_NAME);
    }

    /**
     * @return SimpleXMLElement
     */
    public function current() {
        return simplexml_load_string($this->reader->readOuterXml());
    }
}

Equipped with this iterator the rest of your job is mainly a piece of cake. First load the 10 gigabyte file:

$pc      = "78746";

$xmlfile = '../data/lineups.xml';
$reader  = new XMLReader();
$reader->open($xmlfile);

And then check if the element contains the information and if so, display the data / XML:

foreach (new HeadendIterator($reader) as $headend) {
    /* @var $headend SimpleXMLElement */
    if (!$headend->xpath("/*/postalCodes/postalCode[. = '$pc']")) {
        continue;
    }

    echo 'Found, name: ', $headend->name, "\n";
    echo "==========================================\n";
    $headend->asXML('php://stdout');
}

This does literally what you're trying to achieve: Iterate over the large document (which is memory-friendly) until you find the element(s) you're interested in. You then process on the concrete element and it's XML only; XMLReader::readOuterXml() is a fine tool here.

Exemplary output:

Found, name: Grande Gables at The Terrace
==========================================


        Grande Gables at The Terrace
        Grande Communications
        
            635
        
        
            11111
            22222
            33333
            78746
        
        Austin
        
            
                002
            
            
                003
            
        
        
            
                Thorndale
                Milam
                TX
            
            
                Thrall
                Williamson
                TX