XPath preceding-sibling example

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.