XPath 语法

XPath uses path expressions to select nodes or node-sets in an XML document. The node is selected by following a path or steps.
XPath 通过路径表达式从XML文档中选取节点或节点集。该节点是通过其后的一条语句或相应的步骤选取的。

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The XML Example Document
XML 案例文档

We will use the following XML document in the examples below.
我们将在接下来的案例中引用下面这个XML文档：

<?xml version="1.0" encoding="ISO-8859-1"?>

<bookstore>

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

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

</bookstore>

 

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Selecting Nodes
选取节点

XPath uses path expressions to select nodes in an XML document. The node is selected by following a path or steps. The most useful path expressions are listed below:
XPath使用路径表达式在XML文档中选取节点。该节点是通过其后的一条语句或相应的步骤选取的。下面列出了最常用的路径表达式：

Expression
表达式Description
注释nodenameSelects all child nodes of the node
选取某节点中的所有子节点/Selects from the root node
从根节点处选取//Selects nodes in the document from the current node that match the selection no matter where they are
选取文档中所有匹配的节点，不管该节点位于何处.Selects the current node
选取当前节点..Selects the parent of the current node
选取当前节点的父节点@Selects attributes
选取属性

Examples
案例

In the table below we have listed some path expressions and the result of the expressions:
在下述表格中，我们罗列了一些路径表达式及其运行的结果：

Path Expression
表达式Result
结果bookstoreSelects all the child nodes of the bookstore element
选取bookstore元素的所有子节点/bookstoreSelects the root element bookstore 
选取以bookstore元素为根目录的点

Note: If the path starts with a slash ( / ) it always represents an absolute path to an element!
注意：如果一个路径以（/）开始，那么它代表该元素的绝对路径！

bookstore/bookSelects all book elements that are children of bookstore
选取bookstore中的所有book子元素//bookSelects all book elements no matter where they are in the document
选取文档中的所有book元素bookstore//bookSelects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element
选取文档中所有处于bookstore节点下的book元素//@langSelects all attributes that are named lang
选取所有指定的lang属性

 

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Predicates
条件

Predicates are used to find a specific node or a node that contains a specific value.
它指定了选取节点的范围。

Predicates are always embedded in square brackets.
通常使用方括号[ ]来指定条件。

Examples
实例

In the table below we have listed some path expressions with predicates and the result of the expressions:
在下述表格中，我们列举了一些路径表达式及其运行结果：

Path Expression
表达式Result
结果/bookstore/book[1]Selects the first book element that is the child of the bookstore element
选取bookstore元素下的第一个book元素/bookstore/book[last()]Selects the last book element that is the child of the bookstore element
选取bookstore元素下的最后一个book元素/bookstore/book[last()-1]Selects the last but one book element that is the child of the bookstore element
选取bookstore元素下的倒数第二个book元素/bookstore/book[position()<3]Selects the first two book elements that are children of the bookstore element
选取bookstore元素下的前两个book子元素//title[@lang]Selects all the title elements that have an attribute named lang
选取所含指定的lang属性的有包title元素//title[@lang='eng']Selects all the title elements that have an attribute named lang with a value of 'eng'
选取所有lang属性值为“eng”的所有“title”元素/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
选取bookstore元素下所有price元素值大于35.00的book元素/bookstore/book[price>35.00]/titleSelects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00
选取bookstore元素下所有price元素值大于35.00的book节点下的title元素

 

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Selecting Unknown Nodes
选取未知节点

XPath wildcards can be used to select unknown XML elements.
可以通过 XPath 通配符选取未知的XML元素。

Wildcard
通配符Description
说明*Matches any element node
匹配任意的元素节点@*Matches any attribute node
匹配任意的属性节点node()Matches any node of any kind
匹配所有类型的节点

Examples
案例

In the table below we have listed some path expressions and the result of the expressions:
在下述表格中，我们列出了一些路径表达式及其运行结果：

Path Expression
表达式Result
结果/bookstore/*Selects all the child nodes of the bookstore element
选取bookstore元素中的所有子节点//*Selects all elements in the document
选取文档中的所有元素//title[@*]Selects all title elements which have any attribute
选取包含任意属性的所有title元素

 

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Selecting Several Paths
选取多个路径

By using the | operator in an XPath expression you can select several paths.
你可以同过在表达式中添加“ | ”操作符来选取多个路径。

Examples
案例

In the table below we have listed some path expressions and the result of the expressions:
在下述表格中，我们列举了一些路径表达式及其运行结果：

Path Expression
表达式Result
结果//book/title | //book/priceSelects all the title AND price elements of all book elements
选取book元素中的所有title和price元素//title | //priceSelects all the title AND price elements in the document
选取文档中的所有title元素和price元素/bookstore/book/title | //priceSelects all the title elements of the book element of the bookstore element AND all the price elements in the document
选取bookstore元素中book元素所对应的所有title元素以及文档中所有的price元素