5.Java Parser

8/14/2019 5.Java Parser

1/33

XML Parsers

Parsing


2/33

Parsing XML parsing is required so that our application can

inspect, retrieve and modify the document contents.XML parser program this sits between XMLdocument and our application. In an attempt tostandardize the way parser should work, twospecification has come out, that spells out theinterfaces that an application can expect from aparser:

SAX: the Simple API for XML: SAX processes theXML document a tag at a time and generates events.

DOM: the Document Object Model: describes thedocument as a data-structure in the form of tree. Itfirst loads the entire xml in the form of tree. Then

application can edit any traverse and edit any node.


3/33

SAX Vs. DOM When it comes to fast, efficient reading of XML data,

SAX is hard to beat. It requires little memory, because

it does not construct an internal representation (treestructure) of the XML data. Instead, it simply sendsdata to the application as it is read your applicationcan then do whatever it wants to do with the data it

sees.But you cant go back to an earlier position orleap ahead to a different position.

In general, it works well when you simply wantto read data and have the application act on it.

DOM is not suitable for the above since it has to readthe entire data before it acts on it. Also it requiresmore memory.

But when you need to modify an XML structure

especially when you need to modify it interactively,an in-memory structure like the Document Object


4/33

JAXP APITHE Java API for XML Processing (JAXP) is for processing

XML data using applications written in the Java programming

language.

JAXP leverages the parser standards SAX (Simple API for

XML Parsing) and DOM (Document Object Model) so that you

can choose to parse your data as a stream of events or to build

an object representation of it.JAXP also supports the XSLT (XML Stylesheet Language

Transformations) standard, giving you control over the

presentation of the data and enabling you to convert the data to

other XML documents or to other formats, such as HTML.JAXP also provides namespace support, allowing you to work

with DTDs that might otherwise have naming conflicts.

JAXP comes with standard java SDK.


5/33

Steps to write application

1. Obtain a parser object2. Obtain a source of XML data

3. Give that source to the parser to parse. JAXP has just Interfaces for SAX and DOM

and abstract classes that provide factorymethods for obtaining instances of parserand an XML data source.

4 packages:

org.xml.sax: SAX Distribution org.xml.sax.helper: SAX Distribution org.w3c.dom: DOM in java javax.xml.parsers: JAXP distribution


6/33

SAX Programming model

Not a W3C standard but widely adopted includingIBM and Sun.

The standard SAX distribution for java contains 2

packages: org.xml.sax

org.xml.sax.helpers.

They contain 11 classes and interfaces.


7/33

Classes

Classes related to Parser: org.xml.sax.XMLReader is the interface that

an XML parser's SAX2 driver must implement. It isan Interface for reading an XML document using

callbacks. javax.xml.parsers.SAXParser defines the

API that wraps an XMLReader implementationclass. An instance of this class can be obtainedfrom thejavax.xml.parsers.SAXParserFactory.newSAXParser() method.


8/33

Classes related to application that we write:

Contain interface calledorg.xml.sax.ContentHandler:This is the main interface

that most SAX applications implement.This interface define themethods which the parser class will use as call backs. TheParser class excepts an object of this type to be passed in itsconstructor.

org.xml.sax.helpers.DefaultHandleris a class thatimplements ContentHandler. Default base class for SAX2event handlers.

Exception classes:SAXException,

SAXParserExceptionHelper classes: SAXParserFactory

When parser reaches the end of the document, the only data inthe memory is what your application saved.


9/33

SAX Programming model

XML source

DTD

(optional) SAXParser

calls

handlermethods

startDocument

startElement

characters

endElement

endDocument

etc

output

Class implementing ContentHandler

SAXParserFactory

2.input

2. input

1. creates 2. input

e

v

e

n

t

s


10/33

org.xml.sax.ContentHandler

It is this interface which declares the eventhandling methods of SAX.void characters(char ch[], intstart, int length)

void startDocumentvoid endDocument()public void startElement(String uri,String localName, String qName,

Attributes attributes)void endElement(String uri, StringlocalName, String qName)

void processingInstruction(Stringtarget, String data)


11/33

DefaultHandler andSAXParser

DefaultHandler: The easiest way to implementContentHandler interface is to extend theDefaultHandler class, defined in theorg.xml.sax.helpers package.

SAXParserFactory, SAXParser:SAXParseris an abstract class. The staticnewInstance()method ofSAXParserFactory returns a newconcrete implementation of this class. It throws aParserConfigurationExceptionif it is unable

to produce a parser that matches the specifiedconfiguration of options.

Xerces Parser from Apache: implements the Parserand uses JAXP API (org.apache.xerces.jaxp).


12/33

//Program 1: Counting no. of elements

import java.io.*;

import org.xml.sax.Attributes;

import javax.xml.parsers.SAXParser;

import org.xml.sax.helpers.DefaultHandler;

import javax.xml.parsers.SAXParserFactory;public class CountSax extends DefaultHandler{

public static void main(String s[]) throwsException{

if (s.length !=1){

System.out.println("Usage: cmd filename");

System.exit(0);


13/33

// Use the default (non-validating) parser

SAXParserFactoryfactory=SAXParserFactory.newInstance();

/*Creates a new instance of a SAXParser using the currently

configured factory parameters.*/

SAXParser saxParser=factory.newSAXParser();

File f= new File(s[0]);

if(f.exists())

// Parse the input

saxParser.parse(f,new CountSax());

else

System.out.println("unknown file");

}


14/33

static private int ele=0;

public void startDocument(){ele=0;}

public void startElement(String uri, StringlocalName, String qName, Attributes attrs)

{ ele++;}

public void endDocument(){

System.out.println("Number of elements :"+ele);

}}

Execution:

java CountSax note.xml

Number of elements :4


15/33

/*Program 2: Creating HTML document to represent

note.xml*/

import java.io.*;

import org.xml.sax.*;

import javax.xml.parsers.*;

import org.xml.sax.helpers.DefaultHandler;

public class NoteSax extends DefaultHandler{

PrintWriter out;

public NoteSax()throws Exception{out= new PrintWriter(new BufferedWriter(newFileWriter("note.html")));

}


16/33

public static void main(String s[]) throwsException{

if (s.length !=1){

System.out.println("Usage: cmd filename");

System.exit(0);}

SAXParserFactory

factory=SAXParserFactory.newInstance();

SAXParser saxParser=factory.newSAXParser();

File f= new File(s[0]);

if(f.exists())

saxParser.parse(f,new NoteSax());

else

System.out.println("unknown file");}


17/33

public void startDocument(){}

public void startElement(String uri, StringlocalName, String qName, Attributes attrs){

if(qName.equals("note"))

out.println("Note");

if(qName.equals("to"))out.println(" To, ");

if(qName.equals("from"))

out.println("

-from ");if(qName.equals("body") && (attrs.getLength()>0)){for (int i = 0; i < attrs.getLength(); i++) {

String aName = attrs.getQName(i);

Strin value=attrs. etValue(i);


18/33

if(aName.equals("type")){

if( value.equals("warm"))

out.println("");

if( value.equals("cold"))

out.println("");

if( value.equals("formal"))

out.println(""); }

if(aName.equals("subject"))

out.println("" +value+":");}//end of for

}// end of if

}


19/33

public void endElement(String uri, StringlocalName, String qName, Attributes attrs){

if(qName.equals("body"))

out.println("");

if(qName.equals("from"))

out.println("
");}
public void endDocument(){

out.println("");

out.close();}

public void characters(char buf[], int offs, intl) throws SAXException{

String s = new String(buf, offs, l);

out.println(s+ "
");}}


20/33

you

If today was aperfect day then there would be notomorrowGod

Execution:

java CountSax note.xml

creates note.html

note.xml


21/33

Note

To,

you

Contemplation:

If today was a perfect day then therewould be no tomorrow

-from

God

note.html


22/33

Document object model. It is a standard

produced by W3C .All DOM processing assumes that you haveread and parsed a complete document into

memory so that all parts are equally accessible.The data is represented in the form of tree.

Disadvantages

4.It is pretty clumsy if you want to pick out a fewelements.

5.Memory requirement could get restrictive

DOM


23/33

org.w3c.dom package

Interfaces:Node

Document(extends

Node

):The Documentinterface represents the entire HTML or XMLdocument.

NodeList interface provides the abstractionof an ordered collection of nodes

There are static methods inNode interface tocheck element type.Node.ELEMENT_NODE,Node. CDATA_SECTION_NODE


24/33

Methods

Document Methods:public NodeListgetElementsByTagName(String tagname )

public Element

createElement(String tagName) throwsDOMException

public Comment createComment(String data)public Text createTextNode(String data)

NodeList Methods:public int getLength()public Node item(int index)


25/33

Node Methods:

Methods to access information about current node:

public String getNodeName()public short getNodeType()

public NodeList getChildNodes()

Methods to modify the nodes children

public Node appendChild(Node newChild) throwsDOMException

public Node removeChild(Node oldChild) throwsDOMException

public Node replaceChild(Node newChild,Node oldChild) throws DOMException


26/33

DOM Programming model

XML source

DocumentBuilderNode

DTD

(optional)

Search Mechanism

Output

Recursively search nodes

3.Parse

and build

the tree

Document (DOM)2.input 2.input

DocumentBuilderFactory

1.creates

// Program 1: counting no of elements


27/33

// Program 1: counting no. of elements

import org.w3c.dom.*;

import

javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.DocumentBuilder;

import java.io.*;

public class CountDom{

public static void main(String str[])throwsException{

File f= new File(str[0]);

Node n= readFile(f);

int ele=getElementCount(n);

System.out.println(ele);}


28/33

public static Document readFile(File f) throwsException{

Document d;

DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance();

dbf.setValidating(true);

DocumentBuilder db=dbf.newDocumentBuilder();

d=db.parse(f);

return d;}

public static int getElementCount(Node node){

if(node==null)

return 0;

int sum=0;

boolean


29/33

booleanisElement=(node.getNodeType()==Node.ELEMENT_NODE);

if(isElement)sum=1;

NodeList children= node.getChildNodes();

if(children==null)return sum;

for(int i=0;i


30/33

// Program 2: Adding a comment and a node anddisplaying

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.DocumentBuilder;

import java.io.*;

import org.w3c.dom.*;

public class AddNodeDom{

static Node n1;

static Comment c;

public static void main(String str[])throwsException{

File f= new File(str[0]);

Document n= readFile(f);

setElements(n);


31/33

setElements(n);

display(n);

System.out.println("done");

}

public static Document readFile(File f) throwsException{

Document d;

DocumentBuilderFactory dbf=DocumentBuilderFactory.newInstance();

DocumentBuilder db=dbf.newDocumentBuilder();

d=db.parse(f);

return d;

}


32/33

public static void display(Node node){

if(node.getNodeType()==Node.ELEMENT_NODE)

System.out.print(node.getNodeName()+":");if(node.getNodeType()==Node.TEXT_NODE ||node.getNodeType()==Node.COMMENT_NODE )

System.out.println(node.getNodeValue().trim());


if(children!=null)

for(int i=0;i


33/33

public static void setElements(Node node){

if(node==null) return;

booleanisEle=(node.getNodeType()==Node.ELEMENT_NODE);

if(isEle && node.getNodeName().equals("display-name")) n1= node;

if(isEle && node.getNodeName().equals("servlet"))

{ node.appendChild(c);

node.appendChild(n1);}


if(children!=null)

for(int i=0;i

Documents

5.Java Parser