Java StAX Parser - Query XML Document

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Demo Example

Here is the input xml file that we need to parse −

<?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>

StAXParserDemo.java

package com.howcodex.xml;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Iterator;

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.Characters;
import javax.xml.stream.events.EndElement;
import javax.xml.stream.events.StartElement;
import javax.xml.stream.events.XMLEvent;

public class StAXQueryDemo {
   public static void main(String[] args) {
      boolean bFirstName = false;
      boolean bLastName = false;
      boolean bNickName = false;
      boolean bMarks = false;
      boolean isRequestRollNo = false;
      
      try {
         XMLInputFactory factory = XMLInputFactory.newInstance();
         XMLEventReader eventReader =
         factory.createXMLEventReader(new FileReader("input.txt"));

         String requestedRollNo = "393";
         
         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<Attribute> attributes = startElement.getAttributes();
                  String rollNo = attributes.next().getValue();
                     
                  if(rollNo.equalsIgnoreCase(requestedRollNo)) {
                     System.out.println("Start Element : student");
                     System.out.println("Roll No : " + rollNo);
                     isRequestRollNo = true;
                  }
               } else if (qName.equalsIgnoreCase("firstname")) {
                  bFirstName = true;
               } else if (qName.equalsIgnoreCase("lastname")) {
                  bLastName = true;
               } else if (qName.equalsIgnoreCase("nickname")) {
                  bNickName = true;
               }
               else if (qName.equalsIgnoreCase("marks")) {
                  bMarks = true;
               }
               break;
               
               case XMLStreamConstants.CHARACTERS:
                  Characters characters = event.asCharacters();
               
               if(bFirstName && isRequestRollNo) {
                  System.out.println("First Name: " + characters.getData());
                  bFirstName = false;
               }
               if(bLastName && isRequestRollNo) {
                  System.out.println("Last Name: " + characters.getData());
                  bLastName = false;
               }
               if(bNickName && isRequestRollNo) {
                  System.out.println("Nick Name: " + characters.getData());
                  bNickName = false;
               }
               if(bMarks && isRequestRollNo) {
                  System.out.println("Marks: " + characters.getData());
                  bMarks = false;
               }
               break;
               
               case XMLStreamConstants.END_ELEMENT:
                  EndElement endElement = event.asEndElement();
                  
               if(endElement.getName().getLocalPart().equalsIgnoreCase(
                  "student") && isRequestRollNo) {
                  System.out.println("End Element : student");
                  System.out.println();
                  isRequestRollNo = false;
               }
               break;
            }
         }
      } catch (FileNotFoundException e) {
         e.printStackTrace();
      } catch (XMLStreamException e) {
         e.printStackTrace();
      }
   }
}

This would produce the following result −

Start Element : student
Roll No : 393
First Name: dinkar
Last Name: kad
Nick Name: dinkar
Marks: 85
End Element : student
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