It is better to use StAX parser for creating XML documents rather than using SAX parser. Please refer the Java StAX Parser section for the same.

Java SAX Parser – Modify XML Document

Demo Example

Here is the input XML file that we need to modify by appending <Result>Pass<Result/> at the end of </marks> tag.

<?xml version = "1.0"?>
<class>
   <student rollno = "393">
      <firstname>dinkar</firstname>
      <lastname>kad</lastname>
      <nickname>dinkar</nickname>
      <marks>85</marks>
   </student>
   
   <student rollno = "493">
      <firstname>Vaneet</firstname>
      <lastname>Gupta</lastname>
      <nickname>vinni</nickname>
      <marks>95</marks>
   </student>
   
   <student rollno = "593">
      <firstname>jasvir</firstname>
      <lastname>singn</lastname>
      <nickname>jazz</nickname>
      <marks>90</marks>
   </student>
</class>

SAXModifyDemo.java

package com.adglob.xml;

import java.io.*;
import org.xml.sax.*;
import javax.xml.parsers.*;
import org.xml.sax.helpers.DefaultHandler;

public class SAXModifyDemo extends DefaultHandler {
   static String displayText[] = new String[1000];
   static int numberLines = 0;
   static String indentation = "";

   public static void main(String args[]) {

      try {
         File inputFile = new File("input.txt");
         SAXParserFactory factory = 
         SAXParserFactory.newInstance();
         SAXModifyDemo obj = new SAXModifyDemo();
         obj.childLoop(inputFile);
         FileWriter filewriter = new FileWriter("newfile.xml");
         
         for(int loopIndex = 0; loopIndex < numberLines; loopIndex++) {
            filewriter.write(displayText[loopIndex].toCharArray());
            filewriter.write('\n');
            System.out.println(displayText[loopIndex].toString());
         }
         filewriter.close();
      }
      catch (Exception e) {
         e.printStackTrace(System.err);
      }
   }

   public void childLoop(File input) {
      DefaultHandler handler = this;
      SAXParserFactory factory = SAXParserFactory.newInstance();
      
      try {
         SAXParser saxParser = factory.newSAXParser();
         saxParser.parse(input, handler);
      } catch (Throwable t) {}
   }

   public void startDocument() {
      displayText[numberLines] = indentation;
      displayText[numberLines] += "<?xml version = \"1.0\" encoding = \""+
         "UTF-8" + "\"?>";
      numberLines++;
   }

   public void processingInstruction(String target, String data) {
      displayText[numberLines] = indentation;
      displayText[numberLines] += "<?";
      displayText[numberLines] += target;
      
      if (data != null && data.length() > 0) {
         displayText[numberLines] += ' ';
         displayText[numberLines] += data;
      }
      displayText[numberLines] += "?>";
      numberLines++;
   }

   public void startElement(String uri, String localName, String qualifiedName,
      Attributes attributes) {

      displayText[numberLines] = indentation;

      indentation += "    ";

      displayText[numberLines] += '<';
      displayText[numberLines] += qualifiedName;
      
      if (attributes != null) {
         int numberAttributes = attributes.getLength();

         for (int loopIndex = 0; loopIndex < numberAttributes; loopIndex++) {
            displayText[numberLines] += ' ';
            displayText[numberLines] += attributes.getQName(loopIndex);
            displayText[numberLines] += "=\"";
            displayText[numberLines] += attributes.getValue(loopIndex);
            displayText[numberLines] += '"';
         }
      }
      displayText[numberLines] += '>';
      numberLines++;
   }

   public void characters(char characters[], int start, int length) {
      String characterData = (new String(characters, start, length)).trim();
      
      if(characterData.indexOf("\n") < 0 && characterData.length() > 0) {
         displayText[numberLines] = indentation;
         displayText[numberLines] += characterData;
         numberLines++;
      }
   }

   public void endElement(String uri, String localName, String qualifiedName) {
      indentation = indentation.substring(0, indentation.length() - 4) ;
      displayText[numberLines] = indentation;
      displayText[numberLines] += "</";
      displayText[numberLines] += qualifiedName;
      displayText[numberLines] += '>';
      numberLines++;

      if (qualifiedName.equals("marks")) {
         startElement("", "Result", "Result", null);
         characters("Pass".toCharArray(), 0, "Pass".length());
         endElement("", "Result", "Result");
      }
   }
}

This would produce the following result −

<?xml version = "1.0" encoding = "UTF-8"?>
<class>
   <student rollno = "393">
      <firstname>
         dinkar
      </firstname>
      <lastname>
         kad
      </lastname>
      <nickname>
         dinkar
      </nickname>
      <marks>
         85
      </marks>
      <Result>
         Pass
      </Result>
   </student>
   <student rollno = "493">
      <firstname>
         Vaneet
      </firstname>
      <lastname>
         Gupta
      </lastname>
      <nickname>
         vinni
      </nickname>
      <marks>
         95
      </marks>
      <Result>
         Pass
      </Result>
   </student>
   <student rollno = "593">
      <firstname>
         jasvir
      </firstname>
      <lastname>
         singn
      </lastname>
      <nickname>
         jazz
      </nickname>
      <marks>
         90
      </marks>
      <Result>
         Pass
      </Result>
   </student>
</class>