XPath 语法

XPath 使用路径表达式来选择 XML 文档中的节点或节点集。通过遵循路径或步骤来选择节点。

XML 示例文档

我们将在下面的示例中使用以下 XML 文档。

<?xml version="1.0" encoding="UTF-8"?>

<bookstore>

<book>
<title lang="en">Harry Potter</title>
<price>29.99</price>
</book>

<book>
<title lang="en">Learning XML</title>
<price>39.95</price>
</book>

</bookstore>

选择节点

XPath 使用路径表达式来选择 XML 文档中的节点。通过遵循路径或步骤来选择节点。下面列出了最有用的路径表达式：

Expression	Description
nodename	Selects all nodes with the name "nodename"
/	Selects from the root node
//	Selects nodes in the document from the current node that match the selection no matter where they are
.	Selects the current node
..	Selects the parent of the current node
@	Selects attributes

下表列出了一些路径表达式以及表达式的结果：

Path Expression	Result
bookstore	Selects all nodes with the name "bookstore"
/bookstore	Selects the root element bookstore Note: If the path starts with a slash ( / ) it always represents an absolute path to an element!
bookstore/book	Selects all book elements that are children of bookstore
//book	Selects all book elements no matter where they are in the document
bookstore//book	Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element
//@lang	Selects all attributes that are named lang

谓词

谓词用于查找特定节点或包含特定值的节点。

谓词始终嵌入方括号中。

在下表中，我们列出了一些带有谓词的路径表达式以及表达式的结果：

Path Expression	Result
/bookstore/book[1]	Selects the first book element that is the child of the bookstore element. Note: In IE 5,6,7,8,9 first node is[0], but according to W3C, it is [1]. To solve this problem in IE, set the SelectionLanguage to XPath: In JavaScript: xml.setProperty("SelectionLanguage","XPath");
/bookstore/book[last()]	Selects the last book element that is the child of the bookstore element
/bookstore/book[last()-1]	Selects the last but one book element that is the child of the bookstore element
/bookstore/book[position()<3]	Selects the first two book elements that are children of the bookstore element
//title[@lang]	Selects all the title elements that have an attribute named lang
//title[@lang='en']	Selects all the title elements that have a "lang" attribute with a value of "en"
/bookstore/book[price>35.00]	Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00
/bookstore/book[price>35.00]/title	Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00

选择未知节点

XPath 通配符可用于选择未知的 XML 节点。

Wildcard	Description
*	Matches any element node
@*	Matches any attribute node
node()	Matches any node of any kind

下表列出了一些路径表达式以及表达式的结果：

Path Expression	Result
/bookstore/*	Selects all the child element nodes of the bookstore element
//*	Selects all elements in the document
//title[@*]	Selects all title elements which have at least one attribute of any kind

选择多条路径

通过使用 |在 XPath 表达式中，您可以选择多个路径。

下表列出了一些路径表达式以及表达式的结果：

Path Expression	Result
//book/title \| //book/price	Selects all the title AND price elements of all book elements
//title \| //price	Selects all the title AND price elements in the document
/bookstore/book/title \| //price	Selects all the title elements of the book element of the bookstore element AND all the price elements in the document