In this example we will learn how to use the preceding-sibling function of XPath. We will start with the introduction of XPath – what it is and how to use it, then we will see the working model of ‘preceding-sibling’ function.
Tools and technologies used in this example are Java 1.7, Maven, Intellij.
1. Overview
An XPath expression specifies a pattern that selects a set of XML nodes. XSLT templates then use those patterns when applying transformations. The nodes in an XPath expression refer to more than just elements. They also refer to text and attributes, among other things. In fact, the XPath specification defines an abstract document model that defines seven kinds of nodes:
- Root
- Element
- Text
- Attribute
- Comment
- Processing instruction
- Namespace
XPath also provides rules for converting a node in an XML document object model (DOM) tree to a boolean, double, or string value. XPath is a W3C-defined language and an official W3C recommendation; the W3C hosts the XML Path Language (XPath) Version 1.0 specification.
2. XPath Expressions
An XPath expression is composed of a location path and one or more optional predicates. Expressions may also include XPath variables.
The following is an example of a simple XPath expression:
/Country/City
This example would select the <City> element in an XML document
The preceding-sibling function selects all siblings before the current node
3. Project Structure
Below is the project structure used in this example
4. XLM file
Below is the xml file representing Users. Each user has got a unique UserId, name, address, sex, Date Of Birth and email.
user.xml
<?xml version="1.0" encoding="UTF-8"?>
<Users>
<User>
<UserId>12345</UserId>
<Name>
<FirstName>Maden</FirstName>
<MiddleName>Over</MiddleName>
<Surname>Gulliver</Surname>
</Name>
<Address>
<FirstLineOfAddress>Oxford Street</FirstLineOfAddress>
<SecondLineOfAddress></SecondLineOfAddress>
<City>London</City>
<County>Middlesex</County>
<Country>United Kingdom</Country>
</Address>
<Sex>Male</Sex>
<DateOfBirth>01/02/1967</DateOfBirth>
<Email></Email>
</User>
<User>
<UserId>56789</UserId>
<Name>
<FirstName>Tom</FirstName>
<MiddleName>Cruise</MiddleName>
<Surname>Kidman</Surname>
</Name>
<Address>
<FirstLineOfAddress>Reagent Street</FirstLineOfAddress>
<SecondLineOfAddress></SecondLineOfAddress>
<City>New York</City>
<County></County>
<Country>United States</Country>
</Address>
<Sex>Female</Sex>
<DateOfBirth>02/03/1978</DateOfBirth>
<Email></Email>
</User>
<User>
<UserId>72638</UserId>
<Name>
<FirstName>Amitabh</FirstName>
<MiddleName></MiddleName>
<Surname>Bachchan</Surname>
</Name>
<Address>
<FirstLineOfAddress>Panama Street</FirstLineOfAddress>
<SecondLineOfAddress></SecondLineOfAddress>
<City>Mumbai</City>
<County></County>
<Country>India</Country>
</Address>
<Sex>Male</Sex>
<DateOfBirth>05/04/1999</DateOfBirth>
<Email>amitabh.bachchan@asv.com</Email>
</User>
</Users>5. Java file
Below is the java file which will use XPath to extract information from the User.xml.
ExampleXPathPrecedingSibling.java
package com.javacodegeeks;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import java.io.FileNotFoundException;
import java.io.IOException;
/**
* Example class for XPath preceding-sibling.
* @author JavaCodeGeeks
*/
public class ExampleXPathPrecedingSibling {
DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = null;
public static void main(String q[]) {
ExampleXPathPrecedingSibling exampleXPathPrecedingSibling = new ExampleXPathPrecedingSibling();
exampleXPathPrecedingSibling .execute();
}
public void execute() {
try {
builder = builderFactory.newDocumentBuilder();
Document document = builder.parse(this.getClass().getResourceAsStream("/user.xml"));
XPath xPath = XPathFactory.newInstance().newXPath();
String expression = "//preceding-sibling::User[position()=2]";
NodeList nl = (NodeList) xPath.compile(expression).evaluate(document, XPathConstants.NODESET);
System.out.println(nl.item(0).getTextContent());
System.out.println(nl.item(1).getTextContent());
} catch (ParserConfigurationException e) {
e.printStackTrace();
} catch (SAXException e) {
e.printStackTrace();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (XPathExpressionException e) {
e.printStackTrace();
}
}
}6. Output
Run the ExampleXPathPrecedingSibling.java file. Below is the generated output.
12345 Maden Over Gulliver Oxford Street London Middlesex United Kingdom Male 01/02/1967 56789 Tom Cruise Kidman Reagent Street New York United States Female 02/03/1978
7. Download the source file
This was an example of preceding-sibling function of XPath.
You can download the full source code of this example here : XPath-preceding-sibling
