DOM XML Parser

In Java JDK 2 built-in XML parsers are available.

* DOM

* SAX

DOM XML Parser

The DOM is the easiest to use Java XML Parser. It parses an entire XML document and load it into memory.

pros : modeling it with Object for easy model traversal.

Cons : DOM Parser is slow and consume a lot memory if it load a XML document which contains a lot of data.

       i. DOM parser passes the entire XML document and loads into the memory.

       ii. Then model it is in a “Tree” structure for easy traversal or manipulation.

       By using DOM XML Parser

           * can read a XML file

           * can create a XML file

           * can modify XML file

                  i. Add a new element

                  ii. Update existing element attribute

                  iii. Update existing element value

                  iv. Delete element

           * can count the total number of elements in a XML file. First, search the element name, and then you can use NodeList.getLength() to get the total number of available elements.

package DOMXMLParser;

import java.io.File;

import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.ParserConfigurationException;

import javax.xml.transform.Transformer;

import javax.xml.transform.TransformerException;

import javax.xml.transform.TransformerFactory;

import javax.xml.transform.dom.DOMSource;

import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Attr;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.NamedNodeMap;

import org.w3c.dom.Node;

import org.w3c.dom.NodeList;

import org.xml.sax.SAXException;

public class DOMXMLParserExample {

       /**

       * @param args

       */

      public static void main(String[] args) {

           DOMXMLParserExample xmlFile = new DOMXMLParserExample();

           //read the XML

           xmlFile.readXML();

           //loop node one by one

           xmlFile.loopNodes();

           //write the XML

           xmlFile.writeXML();

           //modify the XML

           xmlFile.modifyXML();

           //count XML elements

           xmlFile.countElements();

     }

     private void readXML(){

          try{

              File fXmlFile = new File("/home/sanjeeva/Desktop/employee.xml");

              DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();

              DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();

              Document doc = dBuilder.parse(fXmlFile);

              doc.getDocumentElement().normalize(); //This is optional; but recommended

              String rootElement = doc.getDocumentElement().getNodeName();

              System.out.println("rootElement --> " + rootElement);

              NodeList nList = doc.getElementsByTagName("staff"); 

 

              System.out.println("----------------------------");

              for (int temp = 0; temp < nList.getLength(); temp++) {

                   Node nNode = nList.item(temp);

                   System.out.println("\nCurrent Element :" + nNode.getNodeName());

                   if (nNode.getNodeType() == Node.ELEMENT_NODE) {

                         Element eElement = (Element) nNode;

                         System.out.println("Staff id : " + eElement.getAttribute("id"));

                         System.out.println("First Name : " + eElement.getEementsByTagName("firstname").item(0).getTextContent());

                         System.out.println("Last Name : " + eElement.getElementsByTagName("lastname").item(0).getTextContent());

                         System.out.println("Designation : " + eElement.getElementsByTagName("designation").item(0).getTextContent());

                         System.out.println("Salary : " + eElement.getElementsByTagName("salary").item(0).getTextContent());

                  }

              }

          }catch (Exception e) {

           e.printStackTrace();

          }

     }

 

     private void loopNodes(){

 

          try{

             File file = new File("/home/sanjeeva/Desktop/employee.xml");

             DocumentBuilder dBuilder =      DocumentBuilderFactory.newInstance().newDocumentBuilder();

             Document doc = dBuilder.parse(file);

             System.out.println("Root element :" + doc.getDocumentElement().getNodeName());

             if (doc.hasChildNodes()) {

                  printNote(doc.getChildNodes());

             }

         }catch (Exception e) {

              e.printStackTrace();

         }

     }

     private void printNote(NodeList nodeList) {

         for (int count = 0; count < nodeList.getLength(); count++) {

              Node tempNode = nodeList.item(count); 

 

              //make sure it's element node.

              if (tempNode.getNodeType() == Node.ELEMENT_NODE) {

                  System.out.println("\nNode Name =" + tempNode.getNodeName() + " [OPEN]");

                  System.out.println("Node Value =" + tempNode.getTextContent());

                  if (tempNode.hasAttributes()) {

                       // get attributes names and values

                       NamedNodeMap nodeMap = tempNode.getAttributes();

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

                            Node node = nodeMap.item(i);

                            System.out.println("attr name : " + node.getNodeName());

                            System.out.println("attr value : " + node.getNodeValue());

                       }

                  }

                  if (tempNode.hasChildNodes()) {

                       //loop again if has child nodes

                       printNote(tempNode.getChildNodes());

                  }

                  System.out.println("Node Name =" + tempNode.getNodeName() + " [CLOSE]");

             }

         }

    }

    private void writeXML(){

 

         try {

            DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();

            DocumentBuilder docBuilder = docFactory.newDocumentBuilder();

 

            // root elements

            Document doc = docBuilder.newDocument();

            Element rootElement = doc.createElement("company");

            doc.appendChild(rootElement);

 

             // staff elements

             Element staff = doc.createElement("Staff");

             rootElement.appendChild(staff);

             // set attribute to staff element

             Attr attr = doc.createAttribute("id");

             attr.setValue("100");

             staff.setAttributeNode(attr);

             // firstname elements

             Element firstname = doc.createElement("firstname");

             firstname.appendChild(doc.createTextNode("Thinuli"));

             staff.appendChild(firstname);

             // lastname elements

             Element lastname = doc.createElement("lastname");

             lastname.appendChild(doc.createTextNode("Pathirana"));

             staff.appendChild(lastname);

             // designation elements

             Element designation = doc.createElement("nickname");

             designation.appendChild(doc.createTextNode("Project Manager"));

             staff.appendChild(designation);

 

             // salary elements

             Element salary = doc.createElement("salary");

             salary.appendChild(doc.createTextNode("100000"));

             staff.appendChild(salary);

   

             // write the content into xml file

             TransformerFactory transformerFactory = TransformerFactory.newInstance();

             Transformer transformer = transformerFactory.newTransformer();

             DOMSource source = new DOMSource(doc);

             StreamResult result = new StreamResult(new File("/home/sanjeeva/Desktop/employeeWrite.xml"));

              // Output to console for testing

              // StreamResult result = new StreamResult(System.out);

              transformer.transform(source, result);

              System.out.println("File saved!");

          } catch (ParserConfigurationException pce) {

               pce.printStackTrace();

          } catch (TransformerException tfe) {

               tfe.printStackTrace();

          }

     }

     private void modifyXML(){

 

           try {

                String filepath = "/home/sanjeeva/Desktop/employeeWrite.xml";

                DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();

                DocumentBuilder docBuilder = docFactory.newDocumentBuilder();

                Document doc = docBuilder.parse(filepath);

                 

                // Get the root element

                Node company = doc.getFirstChild();

                // Get the staff element by tag name directly

                //Node staff = doc.getElementsByTagName("staff").item(0); //

                Node staff = company.getFirstChild();

                // update staff attribute

                NamedNodeMap attr = staff.getAttributes();

                Node nodeAttr = attr.getNamedItem("id");

                nodeAttr.setTextContent("2");

                // append a new node to staff

                Element age = doc.createElement("age");

                age.appendChild(doc.createTextNode("28"));

                staff.appendChild(age);

                    

                // loop the staff child node

                NodeList list = staff.getChildNodes();

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

                     Node node = list.item(i);

                     // get the salary element, and update the value

                     if ("salary".equals(node.getNodeName())) {

                           node.setTextContent("2000000");

                     }

                     //remove firstname

                     if ("firstname".equals(node.getNodeName())) {

                           staff.removeChild(node);

                     }

               }

               // write the content into xml file

               TransformerFactory transformerFactory = TransformerFactory.newInstance();

               Transformer transformer = transformerFactory.newTransformer();

               DOMSource source = new DOMSource(doc);

               StreamResult result = new StreamResult(new File(filepath));

         

               transformer.transform(source, result);

               System.out.println("Modification Done");

         } catch (ParserConfigurationException pce) {

               pce.printStackTrace();

         } catch (TransformerException tfe) {

               tfe.printStackTrace();

         } catch (IOException ioe) {

               ioe.printStackTrace();

         } catch (SAXException sae) {

               sae.printStackTrace();

         }

    }

    private void countElements(){

 

         try {

               String filepath = "/home/sanjeeva/Desktop/employee.xml";

               DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();

               DocumentBuilder docBuilder = docFactory.newDocumentBuilder();

               Document doc = docBuilder.parse(filepath);

    

               NodeList list = doc.getElementsByTagName("staff");

               System.out.println("Total of elements : " + list.getLength());

          } catch (ParserConfigurationException pce) {

                pce.printStackTrace();

          } catch (IOException ioe) {

                ioe.printStackTrace();

          } catch (SAXException sae) {

                sae.printStackTrace();

          }

    }

}

Write XML -

<?xml version="1.0"?>

<company>

<staff id="1001">

<firstname>Sanjeeva</firstname>

<lastname>Pathirana</lastname>

<designation>Software Engineer</designation>

<salary>100000</salary>

</staff>

<staff id="2001">

<firstname>Sandamali</firstname>

<lastname>Silva</lastname>

<designation>Network Engineer</designation>

<salary>200000</salary>

</staff>

</company>