How to read and write xml files?

Question

I have to read and write to and from an XML file. What is the easiest way to read and write XML files using Java?

Answer 1

SAX parser is working differently with a DOM parser, it neither load any XML document into memory nor create any object representation of the XML document. Instead, the SAX parser use callback function org.xml.sax.helpers.DefaultHandler to informs clients of the XML document structure.

SAX Parser is faster and uses less memory than DOM parser. See following SAX callback methods :

startDocument() and endDocument() – Method called at the start and end of an XML document. startElement() and endElement() – Method called at the start and end of a document element. characters() – Method called with the text contents in between the start and end tags of an XML document element.

1. XML file

Create a simple XML file.

    
        yong
        mook kim
        mkyong
        100000
    
    
        low
        yin fong
        fong fong
        200000
    

2. XML parser:

Java file Use SAX parser to parse the XML file.

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

public class ReadXMLFile {
    public static void main(String argv[]) {

        try {
            SAXParserFactory factory = SAXParserFactory.newInstance();
            SAXParser saxParser = factory.newSAXParser();

            DefaultHandler handler = new DefaultHandler() {
                boolean bfname = false;
                boolean blname = false;
                boolean bnname = false;
                boolean bsalary = false;

                public void startElement(String uri, String localName,String qName, 
                            Attributes attributes) throws SAXException {

                    System.out.println("Start Element :" + qName);

                    if (qName.equalsIgnoreCase("FIRSTNAME")) {
                        bfname = true;
                    }

                    if (qName.equalsIgnoreCase("LASTNAME")) {
                        blname = true;
                    }

                    if (qName.equalsIgnoreCase("NICKNAME")) {
                        bnname = true;
                    }

                    if (qName.equalsIgnoreCase("SALARY")) {
                        bsalary = true;
                    }

                }

                public void endElement(String uri, String localName,
                    String qName) throws SAXException {

                    System.out.println("End Element :" + qName);

                }

                public void characters(char ch[], int start, int length) throws SAXException {

                    if (bfname) {
                        System.out.println("First Name : " + new String(ch, start, length));
                        bfname = false;
                    }

                    if (blname) {
                        System.out.println("Last Name : " + new String(ch, start, length));
                        blname = false;
                    }

                    if (bnname) {
                        System.out.println("Nick Name : " + new String(ch, start, length));
                        bnname = false;
                    }

                    if (bsalary) {
                        System.out.println("Salary : " + new String(ch, start, length));
                        bsalary = false;
                    }

                }

            };

            saxParser.parse("c:\\file.xml", handler);

        } catch (Exception e) {
           e.printStackTrace();
        }

    }

}

Result

Start Element :company
Start Element :staff
Start Element :firstname
First Name : yong
End Element :firstname
Start Element :lastname
Last Name : mook kim
End Element :lastname
Start Element :nickname
Nick Name : mkyong
End Element :nickname
and so on...

Source(MyKong) - http://www.mkyong.com/java/how-to-read-xml-file-in-java-sax-parser/