Why is this xmlreader code not working?

问题:

I have a file that looks like this:

    <ExternalPage about="http://animation.about.com/">
       <d:Title>About.com: Animation Guide</d:Title>
       <d:Description>Keep up with developments in online animation for all skill levels.     Download tools, and seek inspiration from online work.</d:Description>
       <topic>Top/Arts/Animation</topic>
    </ExternalPage>
    <ExternalPage about="http://www.toonhound.com/">
       <d:Title>Toonhound</d:Title>
       <d:Description>British cartoon, animation and comic strip creations - links, reviews  and news from the UK.</d:Description>
       <topic>Top/Arts/Animation</topic>
    </ExternalPage>

etc.

I'm trying to get the "about" url, as well as the nested title and description. I've tried the following code, but all I get is a bunch of dashes...

$reader = new XMLReader();

if (!$reader->open("dbpedia/links/xml.xml")) {
die("Failed to open 'xml.xml'");
}
$num=0;
while($reader->read() && $num<200) {
if ($reader->nodeType == XMLReader::ELEMENT && $reader->name == 'ExternalPage') {
$url = $reader->getAttribute('about');

while ($xml->nodeType !== XMLReader::END_ELEMENT ){
$reader->read();

 if ($reader->nodeType == XMLReader::ELEMENT && $reader->name == 'd:Title') {
 $title=$xmlReader->value;
 }
elseif ($reader->nodeType == XMLReader::ELEMENT && $reader->name == 'd:Description') {
$desc=$xmlReader->value;
}
}

}
$num++;echo $url."-".$title."-".$desc."<br />";
}
$reader->close();

I'm new at xmlreader, so I'd appreciate it if someone can figure out what I'm doing wrong.

Note: I'm using xmlreader because the file is a huge one (millions of lines).

EDIT: The beginning of the file looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<RDF xmlns:r="http://www.w3.org/TR/RDF/" xmlns:d="http://purl.org/dc/elements/1.0/"       xmlns="http://dmoz.org/rdf/">
  <!-- Generated at 2013-02-10 00:03:45 EST from DMOZ 2.0 -->
  <Topic r:id="">
<catid>1</catid>
  </Topic>
<Topic r:id="Top/Arts">
    <catid>381773</catid>
  </Topic>
  <Topic r:id="Top/Arts/Animation">
  <catid>423945</catid>
<link1 r:resource="http://www.awn.com/"></link1>
<link r:resource="http://animation.about.com/"></link>
<link r:resource="http://www.toonhound.com/"></link>
<link r:resource="http://enculturation.gmu.edu/2_1/pisters.html"></link>
<link r:resource="http://www.digitalmediafx.com/Features/animationhistory.html"></link>
<link r:resource="http://www.spark-online.com/august00/media/romano.html"></link>
<link r:resource="http://www.animated-divots.net/"></link>
</Topic>
<ExternalPage about="http://www.awn.com/">
<d:Title>Animation World Network</d:Title>
<d:Description>Provides information resources to the international animation community. Features include searchable database archives, monthly magazine, web animation guide, the Animation Village, discussion forums and other useful resources.</d:Description>
<priority>1</priority>
<topic>Top/Arts/Animation</topic>
</ExternalPage>

etc

回答1:

It'll take time and proper debugging to come up with working pure XMLReader code. Meanwhile try this hybrid method:

$xmlR = new XMLReader;
$xmlR->open('dbpedia/links/xml.xml');

//Skip until <ExternalPage> node
while ($xmlR->read() && $xmlR->name !== 'ExternalPage');

$loadedNS_f = false;
while ($xmlR->name === 'ExternalPage')
{
    //Read the entire parent tag with children
    $sxmlNode = new SimpleXMLElement($xmlR->readOuterXML());

    //collect all namespaces in node recursively once; assuming all nodes are similar
    if (!$loadedNS_f) {
        $tagNS = $sxmlNode->getNamespaces(true);
        $loadedNS_f = true; 
    }
    $URL = (string) $sxmlNode['about'];
    $dNS = $sxmlNode->children($tagNS['d']);
    $Title = (string) $dNS->Title;
    $Desc = (string) $dNS->Description;
    $Topic = (string)$sxmlNode->topic;

    var_dump($URL, $Title, $Desc, $Topic);

    // Jump to next <ExternalPage> tag
    $xmlR->next('ExternalPage');
}

$xmlR->close();

回答2:

The reason why it is not working for you is because you only read to the start-tag of the d:Title element and that one got no value:

if ($reader->nodeType == XMLReader::ELEMENT && $reader->name == 'd:Title') {
    $title=$xmlReader->value;
}

You probably wanted to get the nodeValue of that DOM element, but that is not what $xmlReader->value will return. Knowing this there are multiple ways to deal with that:

1. Expand the node (XMLReader::expand()) and get the nodeValue (quick example):

   $title = $reader->expand()->nodeValue;
   

2. Process all XMLReader::TEXT (3) and/or XMLReader::CDATA (4) child-nodes your own (decide if a node is a child-node by looking into XMLReader::$depth).

In any case to streamline your code you can consider to provide what you need directly, for example by creating yourself a set of functions your own or extend the XMLReader class:

class MyXMLReader extends XMLReader
{
    public function readToNextElement()
    {
        while (
            $result = $this->read()
            and $this->nodeType !== self::ELEMENT
        ) ;
        return $result;
    }

    public function readToNext($localname)
    {
        while (
            $result = $this->readToNextElement()
            and $this->localName !== $localname
        ) ;
        return $result;
    }

    public function readToNextChildElement($depth)
    {
        // if the current element is the parent and
        // empty there are no children to go into
        if ($this->depth == $depth && $this->isEmptyElement) {
            return false;
        }

        while ($result = $this->read()) {
            if ($this->depth <= $depth) return false;
            if ($this->nodeType === self::ELEMENT) break;
        }

        return $result;
    }

    public function getNodeValue($default = NULL)
    {
        $node = $this->expand();
        return $node ? $node->nodeValue : $default;
    }
}

You can then just use this extended class to do your processing:

$reader = new MyXMLReader();
$reader->open($uri);

$num = 0;
while ($reader->readToNext('ExternalPage') and $num < 200) {
    $url = $reader->getAttribute('about');

    $depth = $reader->depth;
    $title = $desc = '';

    while ($reader->readToNextChildElement($depth)) {
        switch ($reader->localName) {
            case 'Title':
                $title = $reader->getNodeValue();
                break;
            case 'Description':
                $desc = trim($reader->getNodeValue());
                break;
        }
    }

    $num++;
    echo "#", $num, ": ", $url, " - ", $title, " - ", $desc, "<br />\n";
}

As you can see, this has dramatically made your code much more readable. Also you do not need to care each time if you read this all right.

回答3:

Here's an alternate way to get to that attribute:

$string = file_get_contents($filename);
$xml = new SimpleXMLElement($string);
$result = $xml->xpath('/RDF/ExternalPage[*]/@about');
var_dump($result);