Description
SAX is incredible environment to work in. SAX stands for
Simple API for XML. SAX is an API(Application Programming Interface) which provides a programmatic event-based parsing XML document i.e. it establishes an arena to write programs to the parser.
SAX is created by a group of developers but not W3C whose first version 1.0 was released in May 1998. SAX provides an event-based parser that will expose XML document data for use in a program.
SAX Parser reads the input from the top to bottom. When a certain "event" occur, it invokes call back method that was provided.
As a case, to remove the titles of data articles from a weblog nourish, the starttag() procedure is alluded to as and is checked if "name" component call is available or no more. all things considered, transfer its content. at the point when gotten the occasion name "endtag", investigate if it's far the last detail of "title". at that point overlook all comparably considers until both info closes or another "starttag" with a name of "name" comes nearby.
As it is event based, SAX parser doesn't create any DOM tree structure in memory. SAX parser just checks for an event and call particular call back method in which whatever functionality required, can be implemented and that is how the SAX Parser operates. Description
- SAX parsing is done in one direction i.e. parses node by node from top to bottom.
- it's stream based based processor which have a tiny element in reminiscence at any time.
- Used to read through large XML files as it is not consuming memory.
- SAX runs a little faster than the DOM.
- SAX parser just reads input and tells what it sees and doesn't store XML in memory. So, if needed any structure, all the state-information required should be build up and maintained on own.
- As there is no tree structure, insertion or deletion of a node cannot be done and modification to the structure of the XML tree is not possible.
Example
Initially, create a XML file with the root element 
Output:
[java]
Roll No : 393
First Name: John
Last Name: Mike
Nick Name: Jom
Marks: 85
End Element :student
Roll No : 493
First Name: Rafeal
Last Name: Nadal
Nick Name: Rafa
Marks: 95
End Element :student
Roll No : 593
First Name: Samuel
Last Name: Johnson
Nick Name: Sam
Marks: 90
End Element :student
[/java]
class, student as the child and firstname, lastname, nickname and marks as the sub-childs.
[xml]
<?xml version="1.0"?>
<class>
<student rollno="393">
<firstname>John</firstname>
<lastname>Mike</lastname>
<nickname>Jom</nickname>
<marks>85</marks>
</student>
<student rollno="493">
<firstname>Rafeal</firstname>
<lastname>Nadal</lastname>
<nickname>Rafa</nickname>
<marks>95</marks>
</student>
<student rollno="593">
<firstname>Samuel</firstname>
<lastname>Johnson</lastname>
<nickname>Sam</nickname>
<marks>90</marks>
</student>
</class>
[/xml]
UserHandler.java
[java]
package com.splessons.xml;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
public class UserHandler extends DefaultHandler {
boolean bFirstName = false;
boolean bLastName = false;
boolean bNickName = false;
boolean bMarks = false;
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
if (qName.equalsIgnoreCase("student")) {
String rollNo = attributes.getValue("rollno");
System.out.println("Roll No : " + rollNo);
} 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;
}
}
@Override
public void endElement(String uri, String localName, String qName) throws SAXException {
if (qName.equalsIgnoreCase("student")) {
System.out.println("End Element :" + qName);
}
}
@Override
public void characters(char ch[],
int start, int length) throws SAXException {
if (bFirstName) {
System.out.println("First Name: "
+ new String(ch, start, length));
bFirstName = false;
} else if (bLastName) {
System.out.println("Last Name: "
+ new String(ch, start, length));
bLastName = false;
} else if (bNickName) {
System.out.println("Nick Name: "
+ new String(ch, start, length));
bNickName = false;
} else if (bMarks) {
System.out.println("Marks: "
+ new String(ch, start, length));
bMarks = false;
}
}
}
[/java]
SAXParserDemo.java : In the below code, package org.xml.sax defines SAX interfaces. this bundle characterizes handlerbase-a default execution of a base polish for different handlers.
[java]
package com.splessons.xml;
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 SAXParserDemo {
public static void main(String[] args){
try {
File inputFile = new File("input.txt");
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser saxParser = factory.newSAXParser();
UserHandler userhandler = new UserHandler();
saxParser.parse(inputFile, userhandler);
} catch (Exception e) {
e.printStackTrace();
}
}
}
class UserHandler extends DefaultHandler {
boolean bFirstName = false;
boolean bLastName = false;
boolean bNickName = false;
boolean bMarks = false;
@Override
public void startElement(String uri,
String localName, String qName, Attributes attributes)
throws SAXException {
if (qName.equalsIgnoreCase("student")) {
String rollNo = attributes.getValue("rollno");
System.out.println("Roll No : " + rollNo);
} 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;
}
}
@Override
public void endElement(String uri,
String localName, String qName) throws SAXException {
if (qName.equalsIgnoreCase("student")) {
System.out.println("End Element :" + qName);
}
}
@Override
public void characters(char ch[],
int start, int length) throws SAXException {
if (bFirstName) {
System.out.println("First Name: "
+ new String(ch, start, length));
bFirstName = false;
} else if (bLastName) {
System.out.println("Last Name: "
+ new String(ch, start, length));
bLastName = false;
} else if (bNickName) {
System.out.println("Nick Name: "
+ new String(ch, start, length));
bNickName = false;
} else if (bMarks) {
System.out.println("Marks: "
+ new String(ch, start, length));
bMarks = false;
}
}
}
[/java]
In the above code,
=> package javax.xml.parsers characterizes saxparserfactory superbness which returns saxparser.
=> Saxparserfactory thing produces case of parser. parser interface characterizes the strategy like setdocumenthandler() to setup event handlers and parse() to parse record.
=> Documenthandler interface characterizes startdocument(), enddocument(), startelement(), endelement() and are conjured while xml tag is recognixed and characterizes characters() and summoned while experiences printed content inside the detail.
=> Errorhandler interface characterizes strategies like blunder(), fatalerror(), alert() and are conjured because of different parsing botches.
=> DTD handler interface characterizes methods that are conjured while preparing definitions in a dtd.
=> Entity resolver interface characterizes strategies like resolveentity() is conjured while the parser need to wind up mindful of the certainties related to the guide of a uri.
Key Points
- SAX provides a programmatic event-based parsing XML document.
- SAX Parser reads the input from the top to bottom.