PHP扩展之XML操作（一）——SimpleXML

一、简介及安装

SimpleXML 扩展提供了一个非常简单和易于使用的工具集，能将 XML 转换成一个带有一般属性选择器和数组迭代器的对象。

此扩展需要 libxml PHP 扩展。这表示需要使用 --enable-libxml ，尽管这将隐式完成因为 libxml 是缺省开启的。

需要PHP5及以上版本。

此扩展默认为启用,编译时可通过下列选项禁用： --disable-simplexml

二、使用示例

基本使用

Example #1 Include file example.php with XML string

<?php
$xmlstr = <<<XML
<?xml version='1.0' standalone='yes'?>
<movies>
<movie>
<title>PHP: Behind the Parser</title>
<characters>
<character>
<name>Ms. Coder</name>
<actor>Onlivia Actora</actor>
</character>
<character>
<name>Mr. Coder</name>
<actor>El Act&#211;r</actor>
</character>
</characters>
<plot>
So, this language. It's like, a programming language. Or is it a
scripting language? All is revealed in this thrilling horror spoof
of a documentary.
</plot>
<great-lines>
<line>PHP solves all my web problems</line>
</great-lines>
<rating type="thumbs">7</rating>
<rating type="stars">5</rating>
</movie>
</movies>
XML;
?>

The simplicity of SimpleXML appears most clearly when one extracts a string or number from a basic XML document.

Example #2 Getting <plot>

<?phpinclude 'example.php';
$movies = new SimpleXMLElement($xmlstr);
echo $movies->movie[0]->plot;?>

以上例程会输出：

   So, this language. It's like, a programming language. Or is it a
   scripting language? All is revealed in this thrilling horror spoof
   of a documentary.

Accessing elements within an XML document that contain characters not permitted under PHP's naming convention (e.g. the hyphen) can be accomplished by encapsulating the element name within braces and the apostrophe.

Example #3 Getting <line>

<?phpinclude 'example.php';
$movies = new SimpleXMLElement($xmlstr);
echo $movies->movie->{'great-lines'}->line;?>

以上例程会输出：

PHP solves all my web problems

Example #4 Accessing non-unique elements in SimpleXML

When multiple instances of an element exist as children of a single parent element, normal iteration techniques apply.

<?phpinclude 'example.php';
$movies = new SimpleXMLElement($xmlstr);
/* For each <character> node, we echo a separate <name>. */foreach ($movies->movie->characters->character as $character) {
echo $character->name, ' played by ', $character->actor, PHP_EOL;}
?>

以上例程会输出：

Ms. Coder played by Onlivia Actora
Mr. Coder played by El ActÓr

Note:

Properties ($movies->movie in previous example) are not arrays. They are iterable and accessible objects.

Example #5 Using attributes

So far, we have only covered the work of reading element names and their values. SimpleXML can also access element attributes. Access attributes of an element just as you would elements of an array.

<?phpinclude 'example.php';
$movies = new SimpleXMLElement($xmlstr);
/* Access the <rating> nodes of the first movie.* Output the rating scale, too. */
foreach ($movies->movie[0]->rating as $rating) {
switch((string) $rating['type']) { // Get attributes as element indicescase 'thumbs':echo $rating, ' thumbs up';
break;case 'stars':echo $rating, ' stars';break;}}
?>

以上例程会输出：

7 thumbs up5 stars

Example #6 Comparing Elements and Attributes with Text

To compare an element or attribute with a string or pass it into a function that requires a string, you must cast it to a string using (string). Otherwise, PHP treats the element as an object.

<?phpinclude 'example.php';
$movies = new SimpleXMLElement($xmlstr);
if ((string) $movies->movie->title == 'PHP: Behind the Parser') {print 'My favorite movie.';}
echo htmlentities((string) $movies->movie->title);?>

以上例程会输出：

My favorite movie.PHP: Behind the Parser

Example #7 Comparing Two Elements

Two SimpleXMLElements are considered different even if they point to the same element since PHP 5.2.0.

<?phpinclude 'example.php';
$movies1 = new SimpleXMLElement($xmlstr);$movies2 = new SimpleXMLElement($xmlstr);
var_dump($movies1 == $movies2); // false since PHP 5.2.0?>

以上例程会输出：

bool(false)

Example #8 Using XPath

SimpleXML includes built-in support. To find all <character> elements:

<?phpinclude 'example.php';
$movies = new SimpleXMLElement($xmlstr);
foreach ($movies->xpath('//character') as $character) {
echo $character->name, 'played by ', $character->actor, PHP_EOL;}?>

'//' serves as a wildcard. To specify absolute paths, omit one of the slashes.

以上例程会输出：

Ms. Coder played by Onlivia Actora
Mr. Coder played by El ActÓr

Example #9 Setting values

Data in SimpleXML doesn't have to be constant. The object allows for manipulation of all of its elements.

<?phpinclude 'example.php';$movies = new SimpleXMLElement($xmlstr);
$movies->movie[0]->characters->character[0]->name = 'Miss Coder';
echo $movies->asXML();?>

以上例程会输出：

<?xml version="1.0" standalone="yes"?>
<movies>
 <movie>
  <title>PHP: Behind the Parser</title>
  <characters>
   <character>
    <name>Miss Coder</name>
    <actor>Onlivia Actora</actor>
   </character>
   <character>
    <name>Mr. Coder</name>
    <actor>El Act&#xD3;r</actor>
   </character>
  </characters>
  <plot>
   So, this language. It's like, a programming language. Or is it a
   scripting language? All is revealed in this thrilling horror spoof
   of a documentary.
  </plot>
  <great-lines>
   <line>PHP solves all my web problems</line>
  </great-lines>
  <rating type="thumbs">7</rating>
  <rating type="stars">5</rating>
 </movie>
</movies>

Example #10 Adding elements and attributes

Since PHP 5.1.3, SimpleXML has had the ability to easily add children and attributes.

<?phpinclude 'example.php';$movies = new SimpleXMLElement($xmlstr);
$character = $movies->movie[0]->characters->addChild('character');$character->addChild('name', 'Mr. Parser');
$character->addChild('actor', 'John Doe');
$rating = $movies->movie[0]->addChild('rating', 'PG');$rating->addAttribute('type', 'mpaa');
echo $movies->asXML();?>

以上例程会输出：

<?xml version="1.0" standalone="yes"?>
<movies>
 <movie>
  <title>PHP: Behind the Parser</title>
  <characters>
   <character>
    <name>Ms. Coder</name>
    <actor>Onlivia Actora</actor>
   </character>
   <character>
    <name>Mr. Coder</name>
    <actor>El Act&#xD3;r</actor>
   </character>
  <character><name>Mr. Parser</name><actor>John Doe</actor></character></characters>
  <plot>
   So, this language. It's like, a programming language. Or is it a
   scripting language? All is revealed in this thrilling horror spoof
   of a documentary.
  </plot>
  <great-lines>
   <line>PHP solves all my web problems</line>
  </great-lines>
  <rating type="thumbs">7</rating>
  <rating type="stars">5</rating>
 <rating type="mpaa">PG</rating></movie>
</movies>

Example #11 DOM Interoperability

PHP has a mechanism to convert XML nodes between SimpleXML and DOM formats. This example shows how one might change a DOM element to SimpleXML.

<?php$dom = new DOMDocument;$dom->loadXML('<books><book>
<title>blah</title></book></books>');if (!$dom) {echo 'Error while parsing the document';exit;}
$books = simplexml_import_dom($dom);
echo $books->book[0]->title;?>

以上例程会输出：

blah

处理XML错误

Example #1 Loading broken XML string

<?php
libxml_use_internal_errors(true);
$sxe = simplexml_load_string("<?xml version='1.0'><broken><xml></broken>");
if ($sxe === false) {
echo "Failed loading XML\n";
foreach(libxml_get_errors() as $error) {
echo "\t", $error->message;
}
}
?>

以上例程会输出：

Failed loading XML
    Blank needed here
    parsing XML declaration: '?>' expected
    Opening and ending tag mismatch: xml line 1 and broken
    Premature end of data in tag broken line 1

三、相关函数

• simplexml_import_dom — Get a SimpleXMLElement object from a DOM node.

• simplexml_load_file — Interprets an XML file into an object

• simplexml_load_string — Interprets a string of XML into an object

四、相关类及成员函数

SimpleXMLElement类

• SimpleXMLElement::addAttribute — Adds an attribute to the SimpleXML element

• SimpleXMLElement::addChild — Adds a child element to the XML node

• SimpleXMLElement::asXML — Return a well-formed XML string based on SimpleXML element

• SimpleXMLElement::attributes — Identifies an element's attributes

• SimpleXMLElement::children — Finds children of given node

• SimpleXMLElement::__construct — Creates a new SimpleXMLElement object

• SimpleXMLElement::count — Counts the children of an element

• SimpleXMLElement::getDocNamespaces — Returns namespaces declared in document

• SimpleXMLElement::getName — Gets the name of the XML element

• SimpleXMLElement::getNamespaces — Returns namespaces used in document

• SimpleXMLElement::registerXPathNamespace — Creates a prefix/ns context for the next XPath query

• SimpleXMLElement::saveXML — 别名 SimpleXMLElement::asXML

• SimpleXMLElement::__toString — Returns the string content

• SimpleXMLElement::xpath — Runs XPath query on XML data

SimpleXMLIterator类

• SimpleXMLIterator::current — Returns the current element

• SimpleXMLIterator::getChildren — Returns the sub-elements of the current element

• SimpleXMLIterator::hasChildren — Checks whether the current element has sub elements.

• SimpleXMLIterator::key — Return current key

• SimpleXMLIterator::next — Move to next element

• SimpleXMLIterator::rewind — Rewind to the first element

• SimpleXMLIterator::valid — Check whether the current element is valid

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