如何在 PHP 中使用 XMLReader？

XMLReader is well documented on PHP site. This is a XML Pull Parser, which means it's used to iterate through nodes (or DOM Nodes) of given XML document. For example, you could go through the entire document you gave like this:

<?php
$reader = new XMLReader();
if (!$reader->open("data.xml"))
{
die("Failed to open 'data.xml'");
}
while($reader->read())
{
$node = $reader->expand();
// process $node...
}
$reader->close();
?>

It is then up to you to decide how to deal with the node returned by XMLReader::expand().

It all depends on how big the unit of work, but I guess you're trying to treat each <product/> nodes in succession.

For that, the simplest way would be to use XMLReader to get to each node, then use SimpleXML to access them. This way, you keep the memory usage low because you're treating one node at a time and you still leverage SimpleXML's ease of use. For instance:

$z = new XMLReader;
$z->open('data.xml');


$doc = new DOMDocument;


// move to the first <product /> node
while ($z->read() && $z->name !== 'product');


// now that we're at the right depth, hop to the next <product/> until the end of the tree
while ($z->name === 'product')
{
// either one should work
//$node = new SimpleXMLElement($z->readOuterXML());
$node = simplexml_import_dom($doc->importNode($z->expand(), true));


// now you can use $node without going insane about parsing
var_dump($node->element_1);


// go to next <product />
$z->next('product');
}

Quick overview of pros and cons of different approaches:

XMLReader only

• Pros: fast, uses little memory

• Cons: excessively hard to write and debug, requires lots of userland code to do anything useful. Userland code is slow and prone to error. Plus, it leaves you with more lines of code to maintain

XMLReader + SimpleXML

• Pros: doesn't use much memory (only the memory needed to process one node) and SimpleXML is, as the name implies, really easy to use.

• Cons: creating a SimpleXMLElement object for each node is not very fast. You really have to benchmark it to understand whether it's a problem for you. Even a modest machine would be able to process a thousand nodes per second, though.

XMLReader + DOM

• Pros: uses about as much memory as SimpleXML, and XMLReader::expand() is faster than creating a new SimpleXMLElement. I wish it was possible to use simplexml_import_dom() but it doesn't seem to work in that case

• Cons: DOM is annoying to work with. It's halfway between XMLReader and SimpleXML. Not as complicated and awkward as XMLReader, but light years away from working with SimpleXML.

My advice: write a prototype with SimpleXML, see if it works for you. If performance is paramount, try DOM. Stay as far away from XMLReader as possible. Remember that the more code you write, the higher the possibility of you introducing bugs or introducing performance regressions.

For xml formatted with attributes...

data.xml:

<building_data>
<building address="some address" lat="28.902914" lng="-71.007235" />
<building address="some address" lat="48.892342" lng="-75.0423423" />
<building address="some address" lat="58.929753" lng="-79.1236987" />
</building_data>

php code:

$reader = new XMLReader();


if (!$reader->open("data.xml")) {
die("Failed to open 'data.xml'");
}


while($reader->read()) {
if ($reader->nodeType == XMLReader::ELEMENT && $reader->name == 'building') {
$address = $reader->getAttribute('address');
$latitude = $reader->getAttribute('lat');
$longitude = $reader->getAttribute('lng');
}


$reader->close();

Simple example:


public function productsAction()
{
$saveFileName = 'ceneo.xml';
$filename = $this->path . $saveFileName;
if(file_exists($filename)) {


$reader = new XMLReader();
$reader->open($filename);


$countElements = 0;


while($reader->read()) {
if($reader->nodeType == XMLReader::ELEMENT) {
$nodeName = $reader->name;
}


if($reader->nodeType == XMLReader::TEXT && !empty($nodeName)) {
switch ($nodeName) {
case 'id':
var_dump($reader->value);
break;
}
}


if($reader->nodeType == XMLReader::END_ELEMENT && $reader->name == 'offer') {
$countElements++;
}
}
$reader->close();
exit(print('<pre>') . var_dump($countElements));
}
}

The accepted answer gave me a good start, but brought in more classes and more processing than I would have liked; so this is my interpretation:

$xml_reader = new XMLReader;
$xml_reader->open($feed_url);


// move the pointer to the first product
while ($xml_reader->read() && $xml_reader->name != 'product');


// loop through the products
while ($xml_reader->name == 'product')
{
// load the current xml element into simplexml and we’re off and running!
$xml = simplexml_load_string($xml_reader->readOuterXML());


// now you can use your simpleXML object ($xml).
echo $xml->element_1;


// move the pointer to the next product
$xml_reader->next('product');
}


// don’t forget to close the file
$xml_reader->close();

Most of my XML parsing life is spent extracting nuggets of useful information out of truckloads of XML (Amazon MWS). As such, my answer assumes you want only specific information and you know where it is located.

I find the easiest way to use XMLReader is to know which tags I want the information out of and use them. If you know the structure of the XML and it has lots of unique tags, I find that using the first case is the easy. Cases 2 and 3 are just to show you how it can be done for more complex tags. This is extremely fast; I have a discussion of speed over on What is the fastest XML parser in PHP?

The most important thing to remember when doing tag-based parsing like this is to use if ($myXML->nodeType == XMLReader::ELEMENT) {... - which checks to be sure we're only dealing with opening nodes and not whitespace or closing nodes or whatever.

function parseMyXML ($xml) { //pass in an XML string
$myXML = new XMLReader();
$myXML->xml($xml);


while ($myXML->read()) { //start reading.
if ($myXML->nodeType == XMLReader::ELEMENT) { //only opening tags.
$tag = $myXML->name; //make $tag contain the name of the tag
switch ($tag) {
case 'Tag1': //this tag contains no child elements, only the content we need. And it's unique.
$variable = $myXML->readInnerXML(); //now variable contains the contents of tag1
break;


case 'Tag2': //this tag contains child elements, of which we only want one.
while($myXML->read()) { //so we tell it to keep reading
if ($myXML->nodeType == XMLReader::ELEMENT && $myXML->name === 'Amount') { // and when it finds the amount tag...
$variable2 = $myXML->readInnerXML(); //...put it in $variable2.
break;
}
}
break;


case 'Tag3': //tag3 also has children, which are not unique, but we need two of the children this time.
while($myXML->read()) {
if ($myXML->nodeType == XMLReader::ELEMENT && $myXML->name === 'Amount') {
$variable3 = $myXML->readInnerXML();
break;
} else if ($myXML->nodeType == XMLReader::ELEMENT && $myXML->name === 'Currency') {
$variable4 = $myXML->readInnerXML();
break;
}
}
break;


}
}
}
$myXML->close();
}

This Works Better and Faster For Me

<html>
<head>
<script>
function showRSS(str) {
if (str.length==0) {
document.getElementById("rssOutput").innerHTML="";
return;
}
if (window.XMLHttpRequest) {
// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
} else {  // code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function() {
if (this.readyState==4 && this.status==200) {
document.getElementById("rssOutput").innerHTML=this.responseText;
}
}
xmlhttp.open("GET","getrss.php?q="+str,true);
xmlhttp.send();
}
</script>
</head>
<body>


<form>
<select onchange="showRSS(this.value)">
<option value="">Select an RSS-feed:</option>
<option value="Google">Google News</option>
<option value="ZDN">ZDNet News</option>
<option value="job">Job</option>
</select>
</form>
<br>
<div id="rssOutput">RSS-feed will be listed here...</div>
</body>
</html>

**The Backend File **

<?php
//get the q parameter from URL
$q=$_GET["q"];


//find out which feed was selected
if($q=="Google") {
$xml=("http://news.google.com/news?ned=us&topic=h&output=rss");
} elseif($q=="ZDN") {
$xml=("https://www.zdnet.com/news/rss.xml");
}elseif($q == "job"){
$xml=("https://ngcareers.com/feed");
}


$xmlDoc = new DOMDocument();
$xmlDoc->load($xml);


//get elements from "<channel>"
$channel=$xmlDoc->getElementsByTagName('channel')->item(0);
$channel_title = $channel->getElementsByTagName('title')
->item(0)->childNodes->item(0)->nodeValue;
$channel_link = $channel->getElementsByTagName('link')
->item(0)->childNodes->item(0)->nodeValue;
$channel_desc = $channel->getElementsByTagName('description')
->item(0)->childNodes->item(0)->nodeValue;


//output elements from "<channel>"
echo("<p><a href='" . $channel_link
. "'>" . $channel_title . "</a>");
echo("<br>");
echo($channel_desc . "</p>");


//get and output "<item>" elements
$x=$xmlDoc->getElementsByTagName('item');


$count = $x->length;


// print_r( $x->item(0)->getElementsByTagName('title')->item(0)->nodeValue);
// print_r( $x->item(0)->getElementsByTagName('link')->item(0)->nodeValue);
// print_r( $x->item(0)->getElementsByTagName('description')->item(0)->nodeValue);
// return;


for ($i=0; $i <= $count; $i++) {
//Title
$item_title = $x->item(0)->getElementsByTagName('title')->item(0)->nodeValue;
//Link
$item_link = $x->item(0)->getElementsByTagName('link')->item(0)->nodeValue;
//Description
$item_desc = $x->item(0)->getElementsByTagName('description')->item(0)->nodeValue;
//Category
$item_cat = $x->item(0)->getElementsByTagName('category')->item(0)->nodeValue;




echo ("<p>Title: <a href='" . $item_link
. "'>" . $item_title . "</a>");
echo ("<br>");
echo ("Desc: ".$item_desc);
echo ("<br>");
echo ("Category: ".$item_cat . "</p>");
}
?>