Introduction: SAX parser is the most commonly
used xml parser in Java after DOM. Sax does not load the XML into memory before
parsing it.
JDK provides a SAX parser(SAX
Parser) and DOM builder(document Builder) in package javax.xml.parsers. To
parse XML with SAX, first we need to create a SAX ParserFactory and then get a
SAX Parser from the factory. Then we call parse() method to parse the document.
The parse () takes two parameters- XML file and Callback handler. SAX is an
event-driven API. It defines a set of callback handler methods that will
be invoked when events occur during parsing. JDK provides a Default Handler
class. We override the methods to implement this program
It uses three callback methods
listed below.
startElement(String uri,String localName,String
qName,Attributes attr) : This callback handles when it encounters
an opening tag ‘<’.
endElement(String
uri,String localName,String qName): This
callback handles when it encounters a closing tag ‘>’.
character(char[]
chars,int start, int length):
this callback handles data inside an element.
I’ll use SAX Parser and DOM to parse
the following XML file.
<?xml version="1.0" ?>
<author>Simpson,Adam</author>
<title>XML
Developer's Guide</title>
<genre>Computer</genre>
<price>55.95</price>
<publish_date>2000-10-01</publish_date>
<description>An
in-depth look at creating applications with XML.</description>
</book>
<author>Ray,Smith</author>
<title>C++ for
beginner</title>
<genre>Computer</genre>
<price>35.95</price>
<publish_date>2000-12-16</publish_date>
<description>Start
learning C++. It contains simple example with full explanation</description>
</book>
<author>Ryan,
Kathy</author>
<title>Learn
Hadoop</title>
<genre>Computer</genre>
<price>45.95</price>
<publish_date>2000-11-17</publish_date>
<description>Learn Hadoop.
Learn how to handle big data.</description>
</book>
</catalog>
SAXParser Code:
import
java.io.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
saxparser {
File file=new File("c:\\project\\book.xml");
//constructor
public
saxparser() {
try {
//create an instance of SAXParser Factory
SAXParserFactory
factory=SAXParserFactory.newInstance();
// Get SAXParser from the factory
SAXParser
saxparser=factory.newSAXParser();
//Call parse() to parse the doc.
saxparser.parse(file, new
evntHandler());
} catch(Exception
e)
{
e.printStackTrace();
}
}
public static void
main(String[] args) {
new saxparser();
}
}
import org.xml.sax.SAXException;
import
org.xml.sax.helpers.DefaultHandler;
import java.io.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;
//inner class to handle callback events
public class
evntHandler extends DefaultHandler {
//process the current element
private
String currentElem;
//track # of books
private int cnt=1;
@Override //handles when it finds start tag '<'
public void
startElement(String uri,String localname,String qName,Attributes attr) throws
SAXException {
currentElem=qName;
if(currentElem.equals("book"))
{
System.out.println("book:" + cnt);
cnt++;
}
}
@Override //handles when it finds end tag '>'
public void endElement( String uri,String localName,String qName) throws
SAXException {
currentElem="";
}
@Override //handles data inside element
public void characters(char[] chars, int start, int length) throws SAXException {
if (currentElem.equalsIgnoreCase("title")) {
System.out.println("\tTitle:\t" + new String(chars, start, length));
} else if (currentElem.equalsIgnoreCase("author"))
{
System.out.println("\tAuthor:\t" + new String(chars, start, length));
}
else if (currentElem.equalsIgnoreCase("genre")) {
System.out.println("\tGenre:\t" + new String(chars,start,length));
}
else if (currentElem.equalsIgnoreCase("price")) {
System.out.println("\tPrice:\t
$" + new String(chars,start,length));
}
else if (currentElem.equalsIgnoreCase("publish_date")) {
System.out.println("\tpublish_date:\t
" + new String(chars,start,length));
}
}
}
Output:
Book:1
Author: Simpson,Adam
Title: XML Developer's Guide
Genre: Computer
Price: $55.95
publish_date: 2000-10-01
Book:2
Author: Ray,Smith
Title: C++ for beginner
Genre: Computer
Price: $35.95
publish_date: 2000-12-16
Book:3
Author: Ryan, Kathy
Title: Learn Hadoop
Genre: Computer
Price: $45.95
publish_date: 2000-11-17
DOM:
DOM is a platform- and
language-independent API for processing XML documents. The DOM parser loads the
XML document, builds an object model in the memory, in the form of a tree
comprised of nodes. The DOM API defines the mechanism for querying, traversing
the tree; and adding, modifying and deleting the elements and nodes.
import
java.io.*;
import
javax.xml.parsers.DocumentBuilder;
import
javax.xml.parsers.DocumentBuilderFactory;
import
org.w3c.dom.Document;
import
org.w3c.dom.Element;
import
org.w3c.dom.NodeList;
public class
xmlparser {
public static void main(String[] args)
throws Exception {
DocumentBuilderFactory
factory=DocumentBuilderFactory.newInstance();
DocumentBuilder
docBuilder=factory.newDocumentBuilder();
File file=new File("c:\\project\\book.xml");
Document doc=docBuilder.parse(file);
//get
list of all elements
NodeList list = doc.getElementsByTagName("*");
int bookCount = 0;
for (int i = 0; i < list.getLength();
i++) {
Element element =
(Element)list.item(i);
String nodeName =
element.getNodeName();
if (nodeName.equals("book"))
{
bookCount++;
System.out.println("BOOK: " +
bookCount);
} else if
(nodeName.equals("title")) {
System.out.println("\tTitle:\t"
+
element.getChildNodes().item(0).getNodeValue());
} else if
(nodeName.equals("genre")) {
System.out.println("\tGenre:\t"
+ element.getChildNodes().item(0).getNodeValue());
} else if
(nodeName.equals("price")) {
System.out.println("\tPrice:\t$"
+
element.getChildNodes().item(0).getNodeValue());
} else if (nodeName.equals("publish_date")) {
System.out.println("\tPublish_date:\t"
+
element.getChildNodes().item(0).getNodeValue());
}
}
}
}
BOOK: 1
Title: XML Developer's Guide
Genre: Computer
Price: $55.95
Publish_date: 2000-10-01
BOOK: 2
Title: C++ for beginner
Genre: Computer
Price: $35.95
Publish_date: 2000-12-16
BOOK: 3
Title: Learn Hadoop
Genre: Computer
Price: $45.95
Publish_date: 2000-11-17
