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> |
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 |
| nodename | Selects 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 |
| bookstore | Selects all the child nodes of the bookstore element 选取bookstore元素的所有子节点 |
| /bookstore | Selects 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! |
| bookstore/book | Selects all book elements that are children of bookstore 选取bookstore中的所有book子元素 |
| //book | Selects all book elements no matter where they are in the document 选取文档中的所有book元素 |
| bookstore//book | Selects 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 |
| //@lang | Selects all attributes that are named lang 选取所有指定的lang属性 |
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]/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 选取bookstore元素下所有price元素值大于35.00的book节点下的title元素 |
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 |
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/price | Selects 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 | //price | Selects 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 | //price | Selects 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 |
来源：https://www.cnblogs.com/BlogNetSpace/p/1460148.html