Dom4j queries XML through xpath

1. Get document
   • Saxreader = new saxreader ();
   • Document document = saxreader. Read (fileutil. getfileinputstream (filename ));
2. Query Element
   • String XPath = "/Composites/composite [@ type = 'ondelete']"; // query the composite of the attribute type = 'ondelete'
   • List <element> composites = Document. selectnodes (XPath );
3. XPath syntax

Select Node

XPath uses path expressions to select nodes in XML documents. Nodes are selected by following the path or step.

The most useful path expressions are listed below:

Expression	Description
Nodename	Select all child nodes of this node
/	Select from Root Node
//	Select the nodes in the document from the current node that matches the selected node, regardless of their location
.	Select current node
..	Select the parent node of the current node
@	Select attributes

Instance

In the following table, we have listed some path expressions and expression results:

Path expression	Result
Bookstore	Select All subnodes of the bookstore Element
/Bookstore	Select the root element bookstore Note: If the path starts with a forward slash (/), the path always represents the absolute path to an element!
Bookstore/book	Select the book elements of all the sub-elements of the bookstore.
// Book	Select All book child elements regardless of their location in the document.
Bookstore // book	Select the book elements of all future generations of the bookstore elements, regardless of their location under the bookstore.
// @ Lang	Select all properties named Lang.

Predicates)

It is used to find a specific node or a node that contains a specified value.

The predicates are embedded in square brackets.

Instance

In the following table, we list some path expressions with predicates and the results of the expressions:

Path expression	Result
/Bookstore/book [1]	Select the first book element that belongs to the bookstore sub-element.
/Bookstore/book [last ()]	Select the last book element that belongs to the bookstore sub-element.
/Bookstore/book [last ()-1]	Select the penultimate book element that belongs to the bookstore sub-element.
/Bookstore/book [position () <3]	Select the first two bookstore sub-elements.
// Title [@ Lang]	Select all the title elements with the lang attribute.
// Title [@ lang = 'eng']	Select All title elements and these elements have the lang attribute whose value is Eng.
/Bookstore/book [price> 35.00]	Select the book element of all the bookstore elements, and the value of the price element must be greater than 35.00.
/Bookstore/book [price> 35.00]/Title	Select the title element of the book element in all the bookstore elements, and the value of the price element must be greater than 35.00.

Select unknown Node

The XPath wildcard can be used to select unknown XML elements.

Wildcard	Description
*	Match any element node
@*	Match any attribute node
Node ()	Match any type of Node

Instance

In the following table, we list some path expressions and the results of these expressions:

Path expression	Result
/Bookstore /*	Select All subnodes of the bookstore Element
//*	Select all elements in the document
// Title [@ *]	Select All title elements with attributes.

Select several paths

You can select several paths by using the "|" operator in the path expression.

Instance

In the following table, we list some path expressions and the results of these expressions:

Path expression	Result
// Book/Title | // book/price	Select the title and price of all book elements.
// Title | // price	Select the title and price elements in all documents.
/Bookstore/book/Title | // price	Select the title element of all the book elements that belong to the bookstore element and all the price elements in the document.

XPath axis

The axis defines a node set relative to the current node.

Axis name	Result
Ancestor	Select all the ancestors of the current node (parent, grandfather, etc)
Ancestor-or-self	Select all the founders of the current node (parent, grandfather, etc.) and the current node itself
Attribute	Select all attributes of the current node
Child	Select all child elements of the current node.
Descendant	Select all descendant elements (child, sun, etc.) of the current node ).
Descendant-or-self	Select all descendant elements (child, sun, etc.) of the current node and the current node itself.
Following	Select all nodes after the end label of the current node in the document.
Namespace	Select All namespace nodes of the current node
Parent	Select the parent node of the current node.
Preceding	Select all nodes before the start label of the current node in the document.
Preceding-sibling	Select all peer nodes before the current node.
Self	Select the current node.

Location Path expression

The location path can be absolute or relative.

The absolute path starts with a forward slash (/), but the relative path does not. In either case, the path contains one or more steps, and each step is separated by a slash:

Absolute path:

/step/step/...

Relative Path:

step/step/...

Each step is calculated based on the nodes in the current node set.

Steps include:

Axis)

Define the tree relationship between the selected node and the current node

Node-test)

Recognizes nodes inside a certain axis

Zero or more predicates (predicate)

Further refine the selected node set

Step Syntax:

Axis name: node test [predicates]

Instance

Example	Result
Child: Book	Select the book nodes of all the child elements of the current node
Attribute: Lang	Select the lang attribute of the current node
Child ::*	Select all child elements of the current node
Attribute ::*	Select all attributes of the current node
Child: Text ()	Select all text subnodes of the current node
Child: node ()	Select All subnodes of the current node
Descendant: Book	Select All book descendants of the current node
Ancestor: Book	Select All book predecessors of the current node
Ancestor-or-self: Book	Select all the book predecessors of the current node and the current node (if this node is a book node)
Child: */child: Price	Select all price grandchildren of the current node.

XPath Operators

Operators available in XPath expressions are listed below:

Operator	Description	Instance	Return Value
|	Calculate two node sets	// Book | // CD	Returns all node sets with book and CK elements.
+	Addition	6 + 4	10
-	Subtraction	6-4	2
*	Multiplication	6*4	24
Div	Division	8 Div 4	2
=	Equal	Price = 9.80	If the price is 9.80, true is returned. If the price is 9.90, return fasle.
! =	Not equal	Price! = 9.80	If the price is 9.90, true is returned. If the price is 9.80, return fasle.
<	Less	Price <1, 9.80	If the price is 9.00, true is returned. If the price is 9.90, return fasle.
<=	Less than or equal	Price <= 9.80	If the price is 9.00, true is returned. If the price is 9.90, return fasle.
>	Greater	Price> 9.80	If the price is 9.90, true is returned. If the price is 9.80, return fasle.
> =	Greater than or equal	Price >=9.80	If the price is 9.90, true is returned. If the price is 9.70, return fasle.
Or	Or	Price = 9.80 or price = 9.70	If the price is 9.80, true is returned. If the price is 9.50, return fasle.
And	And	Price> 9.00 and price <9.90	If the price is 9.80, true is returned. If the price is 8.50, return fasle.
MoD	Calculate the remainder of the Division	5 mod 2	1