Xpath 笔记
XPath Document
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Selecting Nodes
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:
Expression |
Description |
nodename |
Selects all child nodes of the named node |
/ |
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 |
Path Expression |
Result |
Bookstore Expression1() |
Selects all the child nodes of the bookstore element |
/bookstore Expression2() |
Selects the root element bookstore Note: If the path starts with a slash ( / ) it always represents(代表) an absolute path to an element! |
bookstore/book Expression3() |
Selects all book elements that are children of bookstore |
//book Expression4() |
Selects all book elements no matter where they are in the document |
bookstore//book Expression5() |
Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element |
//@lang Expression6() |
Selects all attributes that are named lang |
Predicates (断言)
Path Expression |
Result |
/bookstore/book[1] |
Selects the first book element that is the child of the bookstore element. Note: IE5 and later has implemented that [0] should be the first node, but according to the W3C standard it should have been [1]!! |
/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='eng'] |
Selects all the title elements that have an attribute named lang with a value of 'eng' |
/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 |
Selecting Unknown Nodes
XPath wildcards can be used to select unknown XML elements.
Wildcard |
Description |
* |
Matches any element node |
@* |
Matches any attribute node |
node() |
Matches any node of any kind |
Examples:
In the table below we have listed some path expressions and the result of the expressions:
Path Expression |
Result |
/bookstore/* |
Selects all the child nodes of the bookstore element |
//* |
Selects all elements in the document |
//title[@*] |
Selects all title elements which have any attribute |
Selecting Several Paths
By using the | operator in an XPath expression you can select several paths.
Examples:
In the table below we have listed some path expressions and the result of the expressions:
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 |
XPath Axes(轴)
We will use the following XML document in the examples below.
<?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>
|
An axis defines a node-set relative to the current node.
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(前面) |
Selects everything in the document that is before the start tag of the current node |
preceding-sibling(前面的兄弟) |
Selects all siblings before the current node |
self |
Selects the current node |
Location Path Expression
A location path can be absolute or relative.
An absolute location path starts with a slash ( / ) and a relative location path does not. In both cases the location path consists of one or more steps, each separated by a slash:
An absolute location path:
/step/step/...
A relative location path:
step/step/...
|
axisname::nodetest[predicate]
|
Examples:
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 children of the current node |
attribute::* |
Selects all attributes of the current node |
child::text() |
Selects all text child nodes of the current node |
child::node() |
Selects all child nodes 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 |
XPath Operators
An XPath expression returns either a node-set, a string, a Boolean, or a number.
Below is a list of the operators that can be used in XPath expressions:
Operator |
Description |
Example |
Return value |
| |
Computes two node-sets |
//book | //cd |
Returns a node-set with all book and cd elements |
+ |
Addition |
6 + 4 |
10 |
- |
Subtraction |
6 - 4 |
2 |
* |
Multiplication |
6 * 4 |
24 |
div |
Division |
8 div 4 |
2 |
= |
Equal |
price=9.80 |
true if price is 9.80 |
!= |
Not equal |
price!=9.80 |
true if price is 9.90 |
< |
Less than |
price<9.80 |
true if price is 9.00 |
<= |
Less than or equal to |
price<=9.80 |
true if price is 9.00 |
> |
Greater than |
price>9.80 |
true if price is 9.90 |
>= |
Greater than or equal to |
price>=9.80 |
true if price is 9.90 |
or |
or |
price=9.80 or price=9.70 |
true if price is 9.80 |
and |
and |
price>9.00 and price<9.90 |
true if price is 9.80 |
mod |
Modulus (division remainder) |
5 mod 2 |
1 |