dinkar
      kad
      dinkar
      85
   
   
   
      Vaneet
      Gupta
      vinni
      95
   
   
   
      jasvir
      singh
      jazz
      90
   

package com.tutorialspoint.xml;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;

import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLInputFactory;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.events.Attribute;
import javax.xml.stream.events.StartElement;
import javax.xml.stream.events.XMLEvent;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.JDOMException;
import org.jdom2.input.SAXBuilder;
import org.jdom2.output.Format;
import org.jdom2.output.XMLOutputter;

public class StAXModifyDemo {

   public static void main(String[] args) {

      try {
         XMLInputFactory factory = XMLInputFactory.newInstance();
         XMLEventReader eventReader = factory.createXMLEventReader(
            new FileReader("input.txt"));
         SAXBuilder saxBuilder = new SAXBuilder();
         Document document = saxBuilder.build(new File("input.txt"));
         Element rootElement = document.getRootElement();
         List studentElements = rootElement.getChildren("student");

         while(eventReader.hasNext()) {
            XMLEvent event = eventReader.nextEvent();
            
            switch(event.getEventType()) {
               case XMLStreamConstants.START_ELEMENT:
               StartElement startElement = event.asStartElement();
               String qName = startElement.getName().getLocalPart();

               if (qName.equalsIgnoreCase("student")) {
                  Iterator attributes = startElement.getAttributes();
                  String rollNo = attributes.next().getValue();
                  
                  if(rollNo.equalsIgnoreCase("393")) {
                     //get the student with roll no 393

                     for(int i = 0;i < studentElements.size();i++) {
                        Element studentElement = studentElements.get(i);

                        if(studentElement.getAttribute(
                           "rollno").getValue().equalsIgnoreCase("393")) {
                           studentElement.removeChild("marks");
                           studentElement.addContent(new Element("marks").setText("80"));
                        }
                     }
                  }
               }
               break;
            }
         }
         XMLOutputter xmlOutput = new XMLOutputter();

         // display xml
         xmlOutput.setFormat(Format.getPrettyFormat());
         xmlOutput.output(document, System.out);
      } catch (FileNotFoundException e) {
         e.printStackTrace();
      } catch (XMLStreamException e) {
         e.printStackTrace();
      } catch (JDOMException e) {
         e.printStackTrace();
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

   dinkar
   kad
   dinkar
   80


   Vaneet
   Gupta
   vinni
   95


   jasvir
   singh
   jazz
   90