Xpath全称XML Path Language，功能上使用类似路径的语法来识别和导航XML文档中的节点，同时支持HTML语言。XPath是W3C的推荐标准
Nodes#
Xpath中有七种节点：
- element
- attribute
- text
- namespace
- processing-instruction
- comment
- root nodes
选中Nodes#
| 表达式 | 描述 |
|---|
| nodename | 选中所有同名节点 |
| / | 从root node开始选择 |
| // | 从当前节点开始选择，不管层级关系 |
| . | 选择当前节点 |
| .. | 选择当前节点的父节点 |
| @ | 选择属性 |
举例如下
| 表达式 | 效果 |
|---|
| bookstore | Selects all nodes with the name “bookstore” |
| /bookstore | Selects the root element bookstore |
| 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 |
Predicates 谓词#
| Path Expression | Result |
|---|
| /bookstore/book[1] | Selects the first book element that is the child of the bookstore element. |
| /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#
| Wildcard | Description |
|---|
| * | Matches any element node |
| @* | Matches any attribute node |
| node() | Matches any node of any kind |
| 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|或操作符，可以选择多条路径
| 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 |
Axes#
Axes(轴)用来表示和当前节点之间的关系，用于定位树上当前节点的关联节点
| AxisName | Result |
|---|
| ancestor | Selects all ancestors (parent, grandparent, etc.) of the current node |
| ancestor-or-self | Selects all ancestors (parent, grandparent, etc.) of the current node and the current node itself |
| attribute | Selects all attributes of the current node |
| child | Selects all children of the current node |
| descendant | Selects all descendants (children, grandchildren, etc.) of the current node |
| descendant-or-self | Selects all descendants (children, grandchildren, etc.) of the current node and the current node itself |
| following | Selects everything in the document after the closing tag of the current node |
| following-sibling | Selects all siblings after the current node |
| namespace | Selects all namespace nodes of the current node |
| parent | Selects the parent of the current node |
| preceding | Selects all nodes that appear before the current node in the document, except ancestors, attribute nodes and namespace nodes |
| preceding-sibling | Selects all siblings before the current node |
| self | Selects the current node |
路径定位表达式#
- 绝对路径以
/开头 - 定位的语法如下：axisname::nodetest[predicate]
- Axisname轴名称
- Nodetest节点选择
- Predicate 谓词细化选择
| Example | Result |
|---|
| child::book | Selects all book nodes that are children of the current node |
| attribute::lang | Selects the lang attribute of the current node |
| child::* | Selects all element children of the current node |
| attribute::* | Selects all attributes of the current node |
| child::text() | Selects all text node children of the current node |
| child::node() | Selects all children of the current node |
| descendant::book | Selects all book descendants of the current node |
| ancestor::book | Selects all book ancestors of the current node |
| ancestor-or-self::book | Selects all book ancestors of the current node - and the current as well if it is a book node |
| child::*/child::price | Selects all price grandchildren of the current node |
操作符#
Xpath操作符可以返回如下类型的值：
- node-set
- string
- number
- boolean
| Operator | Description | Example |
|---|
| | | Computes two node-sets | //book | //cd |
| + | Addition | 6 + 4 |
| - | Subtraction | 6 - 4 |
| * | Multiplication | 6 * 4 |
| div | Division | 8 div 4 |
| = | Equal | price=9.80 |
| != | Not equal | price!=9.80 |
| < | Less than | price<9.80 |
| <= | Less than or equal to | price<=9.80 |
| > | Greater than | price>9.80 |
| >= | Greater than or equal to | price>=9.80 |
| or | or | price=9.80 or price=9.70 |
| and | and | price>9.00 and price<9.90 |
| mod | Modulus (division remainder) | 5 mod 2 |
Functions函数#
| 函数 | 作用 |
|---|
| name() | 获取node的名称//[starts-with(name(), ‘h’)] |
| text() | 获取node的文本//button[text()=“Submit”] |
| lang(str) | 获取字符串的语言 |
| count() | node计数//table[count(tr)=1] |
| position() | 计算位置//ol/li[position()=2] |
| number() | |
| boolean() | |
| not() | 取反button[not(starts-with(text(),“Submit”))] |
| contains() | 字符串包含font[contains(@class,“head”)] |
| starts-with() | font[starts-with(@class,“head”)] |
| ends-with() | font[ends-with(@class,“head”)] |
| concat(x, y) | |
| substring(str, start, len) | |
浏览器使用示例#
chrome浏览器有两种使用方法：
- Devtool-Elements, CTRL+F
- Devtool-Console,
$x(xpath_syntax)
| 案例 | 解释 |
|---|
| /bookstore/book/title | 选择所有书的title |
| /bookstore/book[1]/title | 选择第一本书的title |
| /bookstore/book/price[text()] | 选择所有书的价格 |
| /bookstore/book[price>35]/price | 选择价格大于35的price节点 |
| /bookstore/book[price>35]/title | 选择价格大于35的title节点 |
$x('//bookstore/book/title')
(4) [title, title, title, title]
$x('//bookstore/book[1]/title')
[title]
$x('//bookstore/book[position() > 2]/title')
(2) [title, title]
$x('//bookstore/book[price > 30]/title')
(2) [title, title]
$x('.//bookstore/book[1]/price')[0].textContent
'30.00'
$x('.//bookstore/book[1]/price[text()]')[0].textContent
'30.00'
$x('.//bookstore/book[1]/price/text()')[0].textContent
'30.00'
$x('.//bookstore/book[@id="testid"]/title')[0].textContent
'Everyday Italian'
$x('.//bookstore/book[@class="testclass"]/title')[0].textContent
'Harry Potter'
$x('.//bookstore/book[contains(@class, "test")]/title')[0].textContent
'Harry Potter'
Xpath测试html打开开发者工具可以试验
Everyday ItalianGiada De Laurentiis
2005
30.00
Harry PotterJ K. Rowling
2005
29.99
XQuery Kick StartJames McGovern
Per Bothner
Kurt Cagle
James Linn
Vaidyanathan Nagarajan
2003
49.99
Learning XMLErik T. Ray
2003
39.95<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
<book id="testid" category="cooking">
<title lang="en">Everyday Italian</title>
<author>Giada De Laurentiis</author>
<year>2005</year>
<price>30.00</price>
</book>
<book class="testclass" category="children">
<title lang="en" href="test.pdf">Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<price>29.99</price>
</book>
<book category="web">
<title lang="en" href="/test">XQuery Kick Start</title>
<author>James McGovern</author>
<author>Per Bothner</author>
<author>Kurt Cagle</author>
<author>James Linn</author>
<author>Vaidyanathan Nagarajan</author>
<year>2003</year>
<price>49.99</price>
</book>
<book category="web">
<title lang="en" href="https://www.google.com">Learning XML</title>
<author>Erik T. Ray</author>
<year>2003</year>
<price>39.95</price>
</book>
</bookstore>
Xpath cheatsheet
XPath Tutorial
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