CS683: Doc 10, SAX, DOM, XSLT

	CS 683 Emerging Technologies Spring Semester, 2003 SAX, DOM, XSLT
	Previous Lecture Notes Index Next © 2003, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 27-Feb-03

Contents of Doc 10, SAX, DOM, XSLT

Creating XML Applications

Document Object Model (DOM)

Simple API for XML (SAX)

Displaying XML

Hello World Example

CD Catalog Example

References
Learning XML , Erik Ray, O'Reilly, 2001

http://www.saxproject.org/

http://www.w3.org/DOM/


Doc 10, SAX, DOM, XSLT Slide # 2

Using XML
Creating XML Applications

Transform XML to display it

Distributed Computing with XML


Doc 10, SAX, DOM, XSLT Slide # 3

Creating XML Applications

Computer program that uses XML

Sample XML applications

uPortal Channels
Microsoft Word

The application usually must

Parse XML
Generate XML
Doc 10, SAX, DOM, XSLT Slide # 4

XML Parsers
A number of XML parsers are available for use in applications

Sun's Java based XML Parser (JAXP)

http://java.sun.com/xml/xml_jaxp.html
Included in JDK 1.4

Xerces from Apache

http://xml.apache.org/

Parsers by Jim Clark

Expat Open source Fast parser written in C http://www.jclark.com/xml/expat.html

XP Java based parser http://www.jclark.com/xml/xp/index.html

VisualWorks Smalltalk includes an XML Parser


Doc 10, SAX, DOM, XSLT Slide # 5

Example of Using Sun's Java XML Parser
File sample.xml
<?xml version="1.0" ?>
<greetings>
<from>
<name>Roger</name>
</from>
<to>
<name>World</name>
</to>
<message>
Hi
</message>
</greetings>


Doc 10, SAX, DOM, XSLT Slide # 6

XMLParseExample.java


import javax.xml.parsers.*; 
import org.xml.sax.*;  
import java.io.*;
import org.w3c.dom.*;
public class Test {
   public static void main(String argv[]) throws Exception {
   DocumentBuilderFactory factory;
   factory = DocumentBuilderFactory.newInstance();
   DocumentBuilder builder = factory.newDocumentBuilder();
   
   Document document;
   document = builder.parse( new File("sample.xml") );
   
   NodeList names = document.getElementsByTagName("name");
   printNodes( names);
   NodeList message = document.getElementsByTagName("message");
   printNodes( message);
   }
   
   public static void printNodes(NodeList list) {
      for (int k = 0; k< list.getLength(); k++ ) {
         Node tag = list.item(k);
         Node child = tag.getFirstChild();
         System.out.print(tag.getNodeName() + "\t");
         System.out.println( child.getNodeValue());
      }
   }
}

Output

name   Roger
name   World
message   
      Hi
Doc 10, SAX, DOM, XSLT Slide # 7

Document Object Model (DOM)
The statement:

builder.parse( new File("sample.xml") );

Converts:

<greetings>
<from>
<name>Roger</name>
</from>
<to>
<name>World</name>
</to>
<message>
Hi
</message>
</greetings>

into the tree structure

Doc 10, SAX, DOM, XSLT Slide # 8

Document Object Model (DOM)

DOM is a W3C standard

The DOM is a platform- and language-neutral interface

Allows programs to

Access XML documents

Modify XML documents

Create XML documents


Doc 10, SAX, DOM, XSLT Slide # 9

Simple API for XML (SAX)

For some applications DOM may be overly complex

SAX is a simpler event driven API for parsing XML

SAX is common in Java XML parsers,

SAX version 1 & 2 exists

Not a W3C standard


Doc 10, SAX, DOM, XSLT Slide # 10

Basic SAX Operation
Your Sax handler class either

Extends org.xml.sax.helpers.DefaultHandler
Implements org.xml.sax.ContentHandler

DefaultHandler

Implements interface org.xml.sax.ContentHandler
Methods implement a default behavior

You register you handler object with the parser

Parse calls back to your object with information about the xml document


Doc 10, SAX, DOM, XSLT Slide # 11

Some Basic Methods in DefaultHandler

 void startDocument () 
          Receive notification of the beginning of the document. 

 void endDocument () 
          Receive notification of the end of the document. 

 void startElement (String  uri, String  localName, String  qName, Attributes  attributes) 
          Receive notification of the start of an element. 

 void endElement (String  uri, String  localName, String qName) 
          Receive notification of the end of an element. 
void characters (char[] ch,  int start, int length) 
          Receive notification of character data inside an element. 

 void ignorableWhitespace (char[] ch, int start, int length) 
          Receive notification of ignorable whitespace in element content. 

 void error (SAXParseException  e) 
          Receive notification of a recoverable parser error. 

 void fatalError (SAXParseException  e) 
          Report a fatal XML parsing error. 

 void warning (SAXParseException  e) 
          Receive notification of a parser warning. 

Doc 10, SAX, DOM, XSLT Slide # 12

SAX 1 Example

import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.Attributes;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.parsers.SAXParser;
import java.util.Vector;
import java.io.File;
   
public class SAXDriverExample extends DefaultHandler
   {
   private Vector root;
   String currentTag;
   
   public static void main(String argv[])
      {
      SAXDriverExample handler = new SAXDriverExample();
   
      // Use the default (non-validating) parser
      SAXParserFactory factory = SAXParserFactory.newInstance();
      try
         {
         SAXParser saxParser = factory.newSAXParser();
         saxParser.parse( new File("sample"), handler );
         }
      catch (Throwable t)
         {
         t.printStackTrace();
         }
      System.out.println( handler.root());
      }
   
Doc 10, SAX, DOM, XSLT Slide # 13
   public void startDocument()
      {
      root = new Vector();
      }
   
   public void characters(char[] ch, int start, int length)
      {
      root.addElement(currentTag + "(" +  new String(ch,start,+length) +      
          ")[" + start+":"+ length+"]\n");
      }
   
   public void startElement(String  uri, String  localName, String qName, 
         Attributes attributes)
      {
      currentTag = qName;
      }
   
   public void endElement(String  uri, String  localName, String qName )
      {
      currentTag = "None";  
      }
   
   public Vector root()
      {
      return root;
      }
   }
Doc 10, SAX, DOM, XSLT Slide # 14

Sample Run
Sample File

<?xml version="1.0" ?>
<Sample>
        <a>hi</a>
        <b>mom</b>
        <b>how are</b>
        <a>you</a>
</Sample>

Output

[Sample(
        )[9:2]
, a(hi)[14:2]
, None(
        )[20:2]
, b(mom)[25:3]
, None(
        )[32:2]
, b(how are)[37:7]
, None(
        )[48:2]
, a(you)[53:3]
, None(
)[60:1]
]
Doc 10, SAX, DOM, XSLT Slide # 15

Validating Example
Modification to Main

        public static void main(String argv[])
                {
                SAXDriverExample handler = new SAXDriverExample();
                SAXParserFactory factory = SAXParserFactory.newInstance();
                factory.setValidating(true);
                try
                        {
                        SAXParser saxParser = factory.newSAXParser();
                        saxParser.parse( new File("sample"), handler );
                        }
                catch (Throwable t)
                        {
                        t.printStackTrace();
                        }
                System.out.println( handler.root());
                }
Doc 10, SAX, DOM, XSLT Slide # 16

Sample

<?xml version="1.0" ?>
<!DOCTYPE Sample [
<!ELEMENT Sample (  ( a* , b*)*)>
<!ELEMENT a (#PCDATA)>
<!ELEMENT b (#PCDATA)> ]>
   
<Sample>
        <a>hi</a>
        <b>mom</b>
        <b>how are</b>
        <a>you</a>
</Sample>

Output

[a(hi)[117:2]
, b(mom)[128:3]
, b(how are)[140:7]
, a(you)[156:3]
]


Doc 10, SAX, DOM, XSLT Slide # 17

SAX 2 Example

import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.helpers.XMLReaderFactory;
import org.xml.sax.InputSource;
import org.xml.sax.XMLReader;
import org.xml.sax.Attributes;
   
import java.util.Vector;
import java.io.FileReader;
   
public class SAXDriverExample extends DefaultHandler
   {
   private Vector root;
   String currentTag;
   
   public static void main(String argv[])
      {
      SAXDriverExample handler = new SAXDriverExample();
      try 
         {
         XMLReader saxParser = XMLReaderFactory.createXMLReader();
         saxParser.setContentHandler( handler);
         saxParser.parse( new InputSource(new FileReader("sample")) );
         } 
      catch (Throwable t) 
         {
         t.printStackTrace();
         }
      System.out.println( handler.root());
      }

Rest of program is the same


Doc 10, SAX, DOM, XSLT Slide # 18

Running the Example

java -Dorg.xml.sax.driver=org.apache.crimson.parser.XMLReaderImpl 
            SAXDriverExample

Output

[a(hi)[139:2]
, b(mom)[150:3]
, b(how are)[162:7]
, a(you)[178:3]
]

The org.xml.sax.driver property can be set inside your program


Doc 10, SAX, DOM, XSLT Slide # 19

Some XML Parsers for Java

gnu.xml.aelfred2.SAXDriver	Lightweight non-validating parser; Free Software
gnu.xml.aelfred2.XmlReader	Optionally validates; Free Software
oracle.xml.parser.v2.SAXParser	Optionally validates; proprietary
org.apache.crimson.parser.XMLReaderImpl	Optionally validates; used in JDK 1.4; Open Source
org.apache.xerces.parsers.SAXParser	Optionally validates; Open Source

The following has links to the above XML parsers

http://www.saxproject.org/?selected=links


Doc 10, SAX, DOM, XSLT Slide # 20

Validating Example

   public static void main(String argv[])
      {
      SAXDriverExample handler = new SAXDriverExample();
      try 
         {
         XMLReader saxParser = XMLReaderFactory.createXMLReader();
         saxParser.setFeature("http://xml.org/sax/features/validation", true);
         saxParser.setContentHandler( handler);
         saxParser.parse( new InputSource(new FileReader("sample")) );
         } 
      catch (Throwable t) 
         {
         t.printStackTrace();
         }
      System.out.println( handler.root());
      }


Doc 10, SAX, DOM, XSLT Slide # 21

Displaying XML

Adding Presentation Layer to XML

Cascading Style Sheets (CSS)

An early presentation layer for Web browsers
Formats and displays XML documents

Extensible Stylesheet Language for Transformation (XSLT)

Presentation layer for XML
Subset of XSL
Used uPortal
Based on transformations rules
A rule matches XML elements
Each rule specifies output in XML

XHTML

A version of HTML that is also XML


Doc 10, SAX, DOM, XSLT Slide # 22

Hello World Example

File hello.xml

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="hello.xsl"?>
<greetings>Hello World</greetings>

File hello.xsl

<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">
<xsl:template match="/">
   <html>
   <body>
      <center><b>
      <xsl:value-of select="greetings"/>
      </b></center>
   </body>
   </html>
</xsl:template>
</xsl:stylesheet>

Instructions
Place both files in the same directory
Open hello.xml with IE 5

Displayed In IEHello World
Doc 10, SAX, DOM, XSLT Slide # 23
Hello World Example ExplainedFile hello.xml

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="hello.xsl"?>
<greetings>Hello World</greetings>

<?xml-stylesheet type="text/xsl" href="hello.xsl"?>

A processing instruction

Tells the application to apply a stylesheet
Gives the type of style sheet: xsl
Gives the location of the style


Doc 10, SAX, DOM, XSLT Slide # 24

Hello World Example ExplainedFile hello.xsl

<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">

xmlns:xsl="http://www.w3.org/TR/WD-xsl"

Declares an XML namespace
Namespaces avoid name collisions

xsl:stylesheet

The name of the tag
The tag "stylesheet" in the xsl name space


Doc 10, SAX, DOM, XSLT Slide # 25

Hello World Example ExplainedFile hello.xsl

<xsl:template match="/">
   <html>
   <body>
      <center><b>
      <xsl:value-of select="greetings"/>
      </b></center>
   </body>
   </html>
</xsl:template>

<xsl:template match="/">

Define a rule that matches all elements
Contents of rule is the output

<xsl:value-of select="greetings"/>

Replaced with the contents of tag "greetings"


Doc 10, SAX, DOM, XSLT Slide # 26

Hello World Example ExplainedOutput of Transformation

 <html>
   <body>
      <center>
         <b>Hello World</b>
      </center>
   </body>
</html>


Doc 10, SAX, DOM, XSLT Slide # 27

CD Catalog Example

Using a Loop
File catalog.xml

<?xml version="1.0" ?> 
<?xml-stylesheet type="text/xsl" href="cd.xsl"?>
<CATALOG>
   <CD>
      <TITLE>Empire Burlesque</TITLE> 
      <ARTIST>Bob Dylan</ARTIST> 
      <COUNTRY>USA</COUNTRY> 
      <COMPANY>Columbia</COMPANY> 
      <PRICE>10.90</PRICE> 
      <YEAR>1985</YEAR> 
   </CD>
   <CD>
      <TITLE>Hide your heart</TITLE> 
      <ARTIST>Bonnie Tyler</ARTIST> 
      <COUNTRY>UK</COUNTRY> 
      <COMPANY>CBS Records</COMPANY> 
      <PRICE>9.90</PRICE> 
      <YEAR>1988</YEAR> 
   </CD>
</CATALOG>
Doc 10, SAX, DOM, XSLT Slide # 28

CD Catalog Example

File cd.xsl

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl">
<xsl:template match="/">
  <html>
  <body>
    <table border="2">
      <tr>
        <th>Title</th>
        <th>Artist</th>
      </tr>
      <xsl:for-each select="CATALOG/CD">
      <tr>
        <td><xsl:value-of select="TITLE"/></td>
        <td><xsl:value-of select="ARTIST"/></td>
      </tr>
      </xsl:for-each>
    </table>
  </body>
  </html>
</xsl:template>
</xsl:stylesheet>

Result Displayed in IE 5

Title	Artist
Empire Burlesque	Bob Dylan
Hide your heart	Bonnie Tyler


Doc 10, SAX, DOM, XSLT Slide # 29

Where to process XSLT
Examples used IE to process XSLT

But

Not all browsers support XSLT
IE was a bit slow in processing the XSLT

Use Web server to process XSLT

Sun's Java API for XML can be used to process XSLT
Web server sends HTML to browser

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