Java Integration

 

 

1. We will start this exercise by refactoring our previous example. Here is the link

2. We will add an additional argument to the getDataFromXML(), a string named xpathXpression

3. Now we will retrieve the NodeList using XPATH. We have libraries that we can use from javax.xml.xpath. 

4. This goes by the following steps. 

• Create a factory object using XPathFactory class. 

• Create a XPath object using the factory. 

• Create an XPathExpression using the xpath object and the expression that we received as the argument. 

• Evaluate the NodeList using the xpath expression. 

 

XPathFactory xfactory = XPathFactory.newInstance();

XPath xpath = xfactory.newXPath();

XPathExpression exp = xpath.compile(xpathXpression);

NodeList list = (NodeList) exp.evaluate(doc, XPathConstants.NODESET);

 

5. In the main method, when invoking the getDataFromXML() add the argument "//item[price > 100]"

List<Items> data  = reader.getDataFromXML(filename, "//item[price > 100]");

 

Here is the final code. 

 

readXMLDOM.java

package com.javatweaks.dom;

 

import java.io.IOException;

import java.util.List;

import javax.xml.parsers.ParserConfigurationException;

import javax.xml.xpath.XPathExpressionException;

import com.javatweaks.sax.read.Items;

 

public class readXMLDOM {

 

    public static void main(String[] args) throws IOException, ParserConfigurationException, XPathExpressionException {

        DOMReader reader = new DOMReader();

        String filename = "C:\\Users\\xxxx\\Documents\\Java_XML\\items.xml";

        List<Items> data  = reader.getDataFromXML(filename, "//item[price > 100]");

        for (Items items : data) {

            System.out.println(items.getManufacturer()+" "+ items.getId() +  " "+ items.getName() +" " + items.getPrice());

        }

        

    }

 

}

 

DOMReader.java

 

package com.javatweaks.dom;

import java.io.File;

import java.io.IOException;

import java.util.ArrayList;

import java.util.List;

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.Element;

import org.w3c.dom.NodeList;

import org.xml.sax.SAXException;

import com.javatweaks.sax.read.Items;

 

public class DOMReader {

    

    public List<Items> getDataFromXML(String filename, String xpathXpression) throws XPathExpressionException  {

        

        List<Items> data = new ArrayList<>();

        File inputFile = new File(filename);

        Document doc = null;

        try {

            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

            DocumentBuilder builder = factory.newDocumentBuilder();

            doc = builder.parse(inputFile);

        } catch (ParserConfigurationException  | SAXException | IOException e) {

            e.printStackTrace();

        }

        

        XPathFactory xfactory = XPathFactory.newInstance();

        XPath xpath = xfactory.newXPath();

        XPathExpression exp = xpath.compile(xpathXpression);

        NodeList list = (NodeList) exp.evaluate(doc, XPathConstants.NODESET);

        //NodeList list = doc.getElementsByTagName("item");

 

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

            Items item = new Items();

            data.add(item);

            Element itemElement = (Element) list.item(i);

            String idString = itemElement.getAttribute(Items.ID);

            item.setId(Integer.parseInt(idString));

            String content = getTextFromElement(itemElement, Items.MAN);

            item.setManufacturer(content);

            content = getTextFromElement(itemElement, Items.NAME);

            item.setName(content);

            content = getTextFromElement(itemElement, Items.PRICE);

            item.setPrice(content);

        }

        

        return data;

        

    }

 

    public String getTextFromElement(Element itemElement, String elementName) {

        Element node = (Element) itemElement.getElementsByTagName(elementName).item(0);

        String content = node.getTextContent();

        return content;

    }

 

}

 

 

The output of the expression that we wanted to evaluate will be 

 

 

Apple Inc 1 iPhone 5 600

Apple Inc 2 iPhone 6 700

Motorola 3 Moto X 200

Motorola 4 Moto G 450

Samsung Corp 5 Samsung S4 550

 

Now if we change the xpath expression to "//item[price >= 600]" the output will be

 

Apple Inc 1 iPhone 5 600

Apple Inc 2 iPhone 6 700

 

This way we have more flexiblity to read the XML file using XPATH.