PHP XML 解析三大流派：DOM、SAX (xml_parse)、SimpleXML 完整對比

PHP XML 解析三大流派：DOM、SAX (xml_parse)、SimpleXML 完整對比

根據文件大小、記憶體限制、查詢靈活度選擇合適解析器。本文以統一範例數據演示三種方式代碼與優缺點。

範例 XML (books.xml)

<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
  <book category="children">
    <title lang="en">Harry Potter</title>
    <author>J K. Rowling</author>
    <year>2005</year>
    <price>29.99</price>
  </book>
  <book category="cooking">
    <title lang="en">Everyday Italian</title>
    <author>Giada De Laurentiis</author>
    <year>2005</year>
    <price>30.00</price>
  </book>
  <book category="web" cover="paperback">
    <title lang="en">Learning XML</title>
    <author>Erik T. Ray</author>
    <year>2003</year>
    <price>39.95</price>
  </book>
</bookstore>

1. DOMDocument (樹模型、隨機訪問、記憶體佔大)

$dom = new DOMDocument();
$dom->load('books.xml');
$books = $dom->getElementsByTagName('book');

foreach ($books as $book) {
    $title = $book->getElementsByTagName('title')->item(0)->textContent;
    $author = $book->getElementsByTagName('author')->item(0)->textContent;
    $year = $book->getElementsByTagName('year')->item(0)->textContent;
    $price = $book->getElementsByTagName('price')->item(0)->textContent;
    echo "$title | $author | $year | $$price\n";
}
// 支援 XPath 查詢
$xpath = new DOMXPath($dom);
$webBooks = $xpath->query('//book[@category="web"]');

優點：完整樹結構、支援 XPath、可修改寫回。缺點：整文檔載入記憶體，大文件 (＞50MB) 易 OOM。

2. XML Parser (SAX 風格、流式、低記憶體、回調複雜)

$parser = xml_parser_create();
xml_parser_set_option($parser, XML_OPTION_CASE_FOLDING, 0);
xml_set_element_handler($parser, 'startElement', 'endElement');
xml_set_character_data_handler($parser, 'charData');

$fp = fopen('books.xml', 'r');
while ($data = fread($fp, 4096)) {
    xml_parse($parser, $data, feof($fp));
}
fclose($fp);
xml_parser_free($parser);

// 回調函數需自行維護狀態機
function startElement($parser, $name, $attrs) { /* 入棧 $name, $attrs */ }
function endElement($parser, $name) { /* 出棧 */ }
function charData($parser, $data) { /* 累加文本 */ }

優點：流式讀取、記憶體恆定、適合超大文件 (GB 級)。缺點：代碼冗長、需手寫狀態機、無法隨機訪問。

3. SimpleXML (簡易、直觀、底層仍是 DOM、中等記憶體)

$xml = simplexml_load_file('books.xml');
foreach ($xml->book as $book) {
    echo "{$book->title} | {$book->author} | {$book->year} | \${$book->price}\n";
    // 屬性訪問
    echo "Category: {$book['category']}\n";
    echo "Lang: {$book->title['lang']}\n";
}
// XPath 支援
$results = $xml->xpath('//book[@category="web"]');

優點：語法極簡、屬性/節點統一為對象屬性、支援 XPath。缺點：大文件同樣載入全部內存、命名空間處理較繁瑣。

選型決策表

XMLReader 範例 (補充)

$reader = new XMLReader();
$reader->open('books.xml');
while ($reader->read()) {
    if ($reader->nodeType == XMLReader::ELEMENT && $reader->name == 'book') {
        $node = simplexml_import_dom($reader->expand());
        echo "{$node->title}\n";
    }
}
$reader->close();