Raja PLECI: How to Create and Evaluate XPath Expression in Java

You can use XPathExpression from javax.xml.xpath package to create and
execute XPATH expression in Java. Java
API provides javax.xml.xpath package, which contains classes like Xpath, XpathFactory to work
with XPATH and XML documents. By the way this is third article on Xpath, In
last couple of tutorials e.g. XPATH examples to select values using
attributes and my XPATH notes for Java programmer,
we have seen basics of Xpath expression from XML and Java point of view. Anyone who has work with XML technologies in
Java knows importance of XPATH, it is one the most useful technology to
retrieve selected data from XML files. XPATH is like SQL which is used to
retrieve data from relational database. Many back-office and middle-office Java
application which transfers data in form of XML documents makes extensive use
of XPATH expression to retrieve value
for printing or for decision making. Though there are lot of open source XML
libraries are available to assist with Java and XML development e.g. XML Beans.
I personally prefer to use standard Java API if functionality is available there. In this Java
tutorial we will learn how to create XPath expression in Java program and retrieving values from XPATH e.g. text, numbers and boolean values, which is
critical for programming flow.

Java
XPATH expression Example

Creating XPATH expression is simple, just navigate to the node you want
to retrieve by putting "/" like in our example if we want to
retrieve models of each smartphone than we will write Xpath expression as /smartphones/smartphone/model. Apart
from navigating to desired node in Xpath expression we have also used utility
method text() to retrieve text and count() to count
number of matching results. Java classes from java.xml.xpath package
e.g. XPath, XPathFactory and XPathExpression is used to
create and evaluate Xpath in Java programming language.

/**

* Java program to demonstrate How to create XPATH expression, How to
execute XPATH

* expression
to retrieve text value, numeric value and boolean value.

*

*/

package test;

import java.io.IOException;

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.XPathExpression;

import javax.xml.xpath.XPathExpressionException;

import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;

import org.w3c.dom.NodeList;

import org.xml.sax.SAXException;

public class
XPathExample {

public void xPathProcessor()
throws SAXException, IOException

, XPathExpressionException, ParserConfigurationException
{

//Create
DocumentBuilderFactory for reading xml file

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

DocumentBuilder builder = factory.newDocumentBuilder();;

Document doc = builder.parse("smartphone.xml");

// Create
XPathFactory for creating XPath Object

XPathFactory xPathFactory = XPathFactory.newInstance();

// Create XPath
object from XPathFactory

XPath xpath = xPathFactory.newXPath();

// Compile the XPath
expression for getting all brands

XPathExpression xPathExpr = xpath.compile("/smartphones/smartphone/brand/text()");

// XPath text
example : executing xpath expression in java

Object result = xPathExpr.evaluate(doc, XPathConstants.NODESET);

System.out.println("Java Xpath text example: All brands of popular
smartphones ");

printXpathResult(result);

//get all models by
xpath expression in java

xPathExpr = xpath.compile("/smartphones/smartphone/model/text()");

result = xPathExpr.evaluate(doc, XPathConstants.NODESET);

System.out.println("Java Xpath text example: All popular smartphone model
");

printXpathResult(result);

// XPath count
example : XPath expression to count elements in xml

xPathExpr = xpath.compile("count(/smartphones/smartphone)");

Double count = (Double) xPathExpr.evaluate(doc, XPathConstants.NUMBER);

System.out.println("XPath count example: How many Smartphones we have:
");

System.out.println("Count of elements: " + count);

// XPath conditional
exampl e: Do we have any HTC smartphone

xPathExpr = xpath.compile("count(/smartphones/smartphone[brand='HTC'])
> 0");

Boolean test = (Boolean) xPathExpr.evaluate(doc, XPathConstants.BOOLEAN);

System.out.println("XPath boolean example: Do we have any HTC smartphone
");

System.out.println(test);

}

public void printXpathResult(Object
result){

NodeList nodes = (NodeList) result;

for (int i =
0; i < nodes.getLength(); i++) {

System.out.println(nodes.item(i).getNodeValue());

}

}

public static void
main(String[]
args) throws
XpathExpressionException

,
ParserConfigurationException, SAXException, IOException
{

XPathExample xPathExample = new XPathExample();

xPathExample.xPathProcessor();

}

}

Output:

Java Xpath text example: All brands of popular smartphones

Apple

Samsung

Nokia

Java Xpath text example: All popular smartphone model

IPhone4S, IPhone4, IPhone5

Galaxy S2, Galaxy nexus, Galaxy Ace

Lumia 800, Lumia 710, Nokia N9

XPath count example: How many
Smartphones we have:

Count of elements: 3.0

XPath boolean
example: Do we have any HTC smartphone

False

That’s all on How to create and evaluate XPath expression in Java .
We have seen How to select XML elements value as text using text() function
and counted matching elements using count() function.
Xpath is real interesting stuff and once you get the basics, its very easy to
work with Xpath both in XML editors and Java programming language.

Other Java and XML tutorials for Java programmers

Difference
between SAX and DOM parser in Java

How
to parse XML files using DOM parser in Java

How
to read XML documents using SAX parser

How
to replace XML meta characters from String in Java

How
to read XML documents using JDOM parser
in Java