Wednesday, April 20, 2016

DOM vs SAX

DOM နှင့် SAX နှစ်ခုစလုံးမှာ သူဟာနှင့်သူ အားသာချက်၊ အားနည်းချက်တွေရှိပါတယ်။

DOM က document structure တစ်ခုလုံးကို memory ပေါ်တင်တဲ့အတွက်ကြောင့် document structure ကြီ:ရင် ကြီးသလောက် memory resource တွေလိုအပ်ပါတယ်။ ဒါပေမဲ့ သူက element တွေ တစ်ခုနှင့်တစ်ခုကြားမှာ အလွယ်တကူသွားလာနိုင်ခြင်း၊ element content တွေကို modify (read/write) လုပ်ရတာလွယ်ကူခြင်းတို့ကြောင့် အသုံးများပါတယ်။ (ဥပမာ - application တစ်ခုရဲ့ system configure file)

SAX ကတော့ document structure တစ်ခုလုံးကို memory ပေါ်မတင်တဲ့အတွက် less-memory intensive ဘဲလိုအပ်ပါတယ်။ SAX ကိုများသောအားဖြင့် element content များတဲ့ XML document တွေကို parse လုပ်တဲ့နေရာမှာအသုံးပြုပါတယ်။ SAX parser တွေက XML document ကို modify (Read only) လုပ်မပေးနိုင်ပါဘူး။ (ဥပမာ directory data file )
DOM
SAX
Read Mode
Reads entire Document
Reads Node by Node
XML File size
Small/Medium XML File
Large XML File
Parser Type
Tree based Parser
Event based Parser
Speed
Little Slow
Faster
Read
Yes
Yes
Write
Yes
No

DOM Parser Java Example Code

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package XML;

import javax.xml.parsers.*;
import java.io.*;
import org.w3c.dom.*;
import org.xml.sax.*;

public class DOMparser {
 
 
 
 public static void main(String [] args){
  try{
   //Read File
   File xmlFile=new File("catalog.xml");
   
   //DocumentBuilderFactory
   DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();
   
   //DocumentBuilder
   DocumentBuilder builder=factory.newDocumentBuilder();
   
   //Document
   Document document=builder.parse(xmlFile);
   
   //Get Root Element
   Element rootElement=document.getDocumentElement();
   
   System.out.println("Root Elemnet :" + rootElement.getTagName());
   
   parseNode(null,rootElement);
   
   
  }catch(Exception e){
   e.printStackTrace();
  }
  
 }
 
 public static void parseNode(Element previousNode,Element visitNode){
  
  if(previousNode != null){
   System.out.println("Element "+ previousNode.getTagName() + " has element :");
  }
  System.out.println("Element Name :" + visitNode.getTagName());
  
  //List Attributes From VisitNode
  if(visitNode.hasAttributes()){
   System.out.println("-Elment " + visitNode.getTagName() +" has Attributes :");
   NamedNodeMap attributes=visitNode.getAttributes();
   
   //Extract Attributes
   for(int i=0; i<attributes.getLength(); i++){
    Attr attribute=(Attr)(attributes.item(i));
    //Print Attribute
    System.out.println("--Attribute :" + attribute.getName() + " = " + attribute.getValue());
   }
  }//End of Attributes List
   
  //Read Nested Element or Child Node
  //Get Child Node List
  NodeList nodeList=visitNode.getChildNodes();
  
  for(int i=0; i<nodeList.getLength(); i++){
   //Get Child Node
   Node node=nodeList.item(i);
   
   if(node.getNodeType()==Node.ELEMENT_NODE){
    Element element=(Element)node;
    
    //Do same Thing /Revcursive Algorithm
    parseNode(visitNode,element);
   }
   else if(node.getNodeType()==Node.TEXT_NODE){
    String str=node.getNodeValue().trim();
    if(str.length()>0){
     System.out.println("---Element Text: " + str);

    }
   }
   
  }
  
  
  
 }


}



SAX Parser Java Example Code


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package XML;

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

public class SAXParser {
 
 public static void main(String []args){
  SAXParser saxParser=new SAXParser();
  saxParser.parseDocument();
 }
 
 public void parseDocument(){
  try{
   //SAX Parser Factory
   SAXParserFactory factory=SAXParserFactory.newInstance();
   
   //SAX Parser
   SAXParser parser=factory.newSAXParser();
   
   //Handler **
   DefaultHandler handler=new CustomSAXHandler();
   //Set File to Parse and Set Handler
   parser.parse(new File("catalog.xml"), handler);
   
   
  }catch(Exception e){
   e.printStackTrace();
  }
 }
 
 private class CustomSAXHandler extends DefaultHandler {
  //Constructor
  public CustomSAXHandler(){
   
  }
  
  //Start Document
  public void startDocument() throws SAXException {
   System.out.println("Event Type : Start Document ");
  }
  
  //End Document
  public void endDocument() throws SAXException {
     System.out.println("Event Type : End Document ");
  }
    
  //Start Element
  public void startElement (String uri,String localName,String qName,Attributes attributes){
   System.out.println("Event Type: Start Element");
   System.out.println("Element Name:" + qName);
   for (int i = 0; i < attributes.getLength(); i++) {
   System.out.println("Attribute Name:" + attributes.getQName(i));
   System.out.println("Attribute Value:" + attributes.getValue(i));
   }
  }
  
  //End Element
  public void endElement(String uri, String localName, String qName)
    throws SAXException {
    System.out.println("Event Type: End Element");
  }
  
  //Get Text
  public void characters(char[] ch, int start, int length)
    throws SAXException {
    System.out.println("Event Type: Text");
    String str = (new String(ch, start, length));
    System.out.println(str);
  }
  
  //Error
  public void error(SAXParseException e)
    throws SAXException{
    System.out.println("Error "+e.getMessage());
  }
  public void fatalError(SAXParseException e)
    throws SAXException{
    System.out.println("Fatal Error "+e.getMessage());
  }
  public void warning(SAXParseException e)
    throws SAXException{
    System.out.println("Warning "+e.getMessage());
  }


 }

}

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