XML parsing and generation in PHP

XML (Extensible Markup Language) is a commonly used data exchange format that can be parsed and generated by a variety of programming languages. This article will introduce XML parsing and generation in PHP.

1. Basic concepts of XML

Before starting XML parsing and generation in PHP, you need to understand some basic concepts of XML:

1. Tag (element ): The basic unit in XML, consisting of a start tag, an end tag and the content between them.
2. Attribute: Additional information in the tag, consisting of attribute name and attribute value, stored in the start tag.
3. Namespace (namespace): A name used to distinguish the same element or attribute in different XML documents.
4. XML declaration: Specify the version and encoding method of the XML document.

2. XML parsing in PHP

PHP provides a variety of methods for parsing XML documents, including two commonly used methods, SimpleXML and DOMDocument.

1. SimpleXML

SimpleXML is a simple method provided by PHP to parse XML documents. It parses the XML document into an object, and can obtain and manipulate the elements and attributes of the XML document through the properties and methods of the object.

The following is a simple example that demonstrates how to use SimpleXML to parse an XML document:

// 读取XML文件
$xml = simplexml_load_file('books.xml');

// 遍历books元素并输出book元素的属性和内容
foreach ($xml->books->book as $book) {
    echo '书名：' . $book['name'] . '<br>';
    echo '作者：' . $book['author'] . '<br>';
    echo '价格：' . $book->price . '<br>';
    echo '<br>';
}

In the above example, use the simplexml_load_file function to read the XML file books.xml and parse it into a SimpleXMLElement object, and then traverses all book elements under the books element through a foreach loop to obtain the attributes and content of the book element.

2. DOMDocument

DOMDocument is a method of parsing XML documents based on DOM (Document Object Model) provided by PHP. It parses the entire XML document into a tree, and can obtain and manipulate the elements and attributes of the XML document through the hierarchical structure of nodes.

The following is a simple example that demonstrates how to use DOMDocument to parse an XML document:

// 读取XML文件
$doc = new DOMDocument();
$doc->load('books.xml');

// 遍历books元素并输出book元素的属性和内容
$books = $doc->getElementsByTagName('books')->item(0);
foreach ($books->getElementsByTagName('book') as $book) {
    echo '书名：' . $book->getAttribute('name') . '<br>';
    echo '作者：' . $book->getAttribute('author') . '<br>';
    echo '价格：' . $book->getElementsByTagName('price')->item(0)->nodeValue . '<br>';
    echo '<br>';
}

In the above example, the DOMDocument class is used to read the XML file books.xml and parse it into a DOMDocument object. Get the books element in the document through the getElementsByTagName method and traverse all book elements below it to obtain the attributes and content of the book element.

3. XML generation in PHP

In addition to parsing XML documents, PHP also provides a variety of methods for generating XML documents.

1. SimpleXML

Same as parsing, when using SimpleXML to generate an XML document, XML elements are also organized into objects. First create a SimpleXMLElement object, then add child elements and attributes by calling its addChild method, and finally convert the SimpleXMLElement object into an XML string by calling the asXML method.

The following is a simple example that demonstrates how to use SimpleXML to generate an XML document:

// 创建SimpleXMLElement对象
$xml = new SimpleXMLElement('<?xml version="1.0" encoding="UTF-8"?><books></books>');

// 添加book元素和属性
$book1 = $xml->addChild('book');
$book1->addAttribute('name', 'PHP入门');
$book1->addAttribute('author', '张三');
$book1->addChild('price', '29.99');

$book2 = $xml->addChild('book');
$book2->addAttribute('name', 'PHP进阶');
$book2->addAttribute('author', '李四');
$book2->addChild('price', '39.99');

// 输出XML文档
echo $xml->asXML();

In the above example, create an empty SimpleXMLElement object and add book elements and attributes through the addChild method , and finally convert the SimpleXMLElement object into an XML string and output it.

2. DOMDocument

Similarly, when using DOMDocument to generate an XML document, XML elements are also organized into nodes. Use the DOMDocument class to create a DOMDocument object, then create element nodes and attribute nodes through the createElement method, and add them to the document through the appendChild method, and finally save the DOMDocument object as an XML file through the saveXML or save method.

The following is a simple example that demonstrates how to use DOMDocument to generate an XML document:

// 创建DOMDocument对象
$doc = new DOMDocument('1.0', 'UTF-8');

// 创建根元素
$root = $doc->createElement('books');
$doc->appendChild($root);

// 创建book元素和属性
$book1 = $doc->createElement('book');
$book1->setAttribute('name', 'PHP入门');
$book1->setAttribute('author', '张三');
$root->appendChild($book1);

$price1 = $doc->createElement('price', '29.99');
$book1->appendChild($price1);

$book2 = $doc->createElement('book');
$book2->setAttribute('name', 'PHP进阶');
$book2->setAttribute('author', '李四');
$root->appendChild($book2);

$price2 = $doc->createElement('price', '39.99');
$book2->appendChild($price2);

// 输出XML文件
$doc->save('books.xml');

In the above example, create a new DOMDocument object and create a root element named books . Create book elements and attributes via the createElement method and add them to the document using the appendChild method. Finally, use the save method to save the DOMDocument object as an XML file.

4. Summary

This article introduces XML parsing and generation in PHP, including using SimpleXML and DOMDocument to parse XML documents, and using SimpleXML and DOMDocument to generate XML documents. When using XML parsing and generation, you need to understand the basic concepts of XML, including tags, attributes, namespaces, and XML declarations. Choosing the appropriate method according to actual needs can make processing XML data more convenient.

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