PHP DOMDocument 完整教學：XML 文檔操作指南

簡介

DOM (Document Object Model) 是 W3C 標準，提供對 HTML/XML 文檔的結構化物件模型與操作介面。PHP 內建 DOMDocument、DOMXPath 等類別，支援載入、驗證、查詢、修改、建立、序列化 XML。屬於樹狀解析器，將整份文檔載入記憶體形成節點樹。

安裝

PHP 核心內建，無需安裝。

核心類別與方法速查

DOMXPath 常用方法

• new DOMXPath($doc) — 建立 XPath 查詢器
• query($expression) — 執行 XPath 查詢，返回 DOMNodeList
• evaluate($expression) — 執行 XPath 表達式，可返回標量值
• registerNamespace($prefix, $uri) — 註冊命名空間前綴

實用範例

XML 範例 (note.xml)

<?xml version="1.0" encoding="ISO-8859-1"?>
<note>
    <to>Tove</to>
    <from>Jani</from>
    <heading>Reminder</heading>
    <body>Don't forget me this weekend!</body>
</note>

1. 載入並輸出完整 XML

<?php
$doc = new DOMDocument();
$doc->load('note.xml');
echo $doc->saveXML();
?>

2. 遍歷根元素子節點

<?php
$doc = new DOMDocument();
$doc->load('note.xml');
$root = $doc->documentElement; // 
foreach ($root->childNodes as $node) {
    if ($node->nodeType === XML_ELEMENT_NODE) {
        echo $node->nodeName . ' = ' . $node->nodeValue . '<br>';
    }
}
/* 輸出:
to = Tove
from = Jani
heading = Reminder
body = Don't forget me this weekend!
*/
?>

3. XPath 查詢

<?php
$doc = new DOMDocument();
$doc->load('books.xml');
$xpath = new DOMXPath($doc);
$titles = $xpath->query('//book[@category="php"]/title');
foreach ($titles as $title) {
    echo $title->nodeValue . '<br>';
}
?>

4. 建立新 XML 文檔

<?php
$doc = new DOMDocument('1.0', 'UTF-8');
$root = $doc->createElement('catalog');
$doc->appendChild($root);

$book = $doc->createElement('book');
$book->setAttribute('id', '1');
$root->appendChild($book);

$title = $doc->createElement('title', 'PHP Mastery');
$book->appendChild($title);

$author = $doc->createElement('author');
$author->appendChild($doc->createTextNode('John Doe'));
$book->appendChild($author);

echo $doc->saveXML();
?>

5. 修改現有 XML

<?php
$doc = new DOMDocument();
$doc->load('note.xml');
$xpath = new DOMXPath($doc);
$toNode = $xpath->query('//to')->item(0);
if ($toNode) {
    $toNode->nodeValue = 'Anna';
}
$dateNode = $doc->createElement('date', '2024-01-15');
$doc->documentElement->appendChild($dateNode);
$doc->save('note_updated.xml');
?>

6. 處理命名空間

<?php
$doc = new DOMDocument();
$doc->load('ns.xml');
$xpath = new DOMXPath($doc);
$xpath->registerNamespace('dc', 'https://purl.org/dc/elements/1.1/');
$creators = $xpath->query('//dc:creator');
foreach ($creators as $c) {
    echo $c->nodeValue . '<br>';
}
?>

空白文字節點注意事項

XML 格式化時的縮排、換行會產生 #text 空白節點。遍歷時請檢查 $node->nodeType === XML_ELEMENT_NODE (值為 1) 以過濾純元素節點，或呼叫 $doc->preserveWhiteSpace = false; $doc->formatOutput = true; 配合 normalize() 整理。

選擇建議：DOM vs SimpleXML vs XMLReader