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
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 | <?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
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 | 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.
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | 12345MadenOverGulliverOxford StreetLondonMiddlesexUnited KingdomMale01/02/196756789TomCruiseKidmanReagent StreetNew YorkUnited StatesFemale02/03/1978 |
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
