TECH854 XML TECHNOLOGIES Programming with XML

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TECH854XML TECHNOLOGIESProgramming with XML

• Gillian Miller
• gillian_at_ics.mq.edu.au
• Room 378

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PROGRAMMING WITH XML

• Week 5 Parsing XML - SAX
• Week 6 XML to objects - DOM
• Week 7 XML Web Applications
• Week 8 XML Integration, Data Exchange and
  Databases
• Making XML work in real applications
• This part of the course requires programming (ie
  Java) and assumes programming expertise
• Plenty of examples and code tempates

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Microsoft
Java
IBM
XML Mediator
Java
Web Online Inventory
XML
Warehouse Oracle
Web Server Apache
HTML
Web Server
Java
XML
Web Online Shopping
XML Transformers
Web Content Management
XML Content
XML is format for data exchange and content
management
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Why JAVA ?

• Portability - Java Virtual machine
• Web and Application Services - J2EE standards
• Object-Oriented Language - logical and easy to
  program
• Java playing increasing role in e-commerce,
  application integration and large information
  systems arena
• Industrial strength capabilities
• Scaleability
• Security model
• Performance (good middle ground)
• Multithreading
• Java includes extensive library of frameworks and
  interfaces (the API) - JDBC, JAXP, Servlets, JSP,
  JAXB

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XML and Java Alphabet soup
JavaBean
Java
RMI
DTD
JDK
XML
JDBC
EJB
XML-Schema
Servlets
DOM
Java WSDK
JavaDoc
JAXP
JSP
JDOM
SAX
JAX-RPC
XSLT
JAXM
WSDL
Soap
JAXR
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Java Prerequisites
public class HelloWorld public String
getHello() return Helloo public
static void main (String args) int
j2 System.out.println( Hello World
) System.out.println( getHello() j
)
What is wrong with these programs ?
public class MyCar Color carColor
public void setColor (Color color)
this.carColor color public static
void main(String args) MyCar car
car.setColor(Color.green)
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Java Prerequisites

• Classes, Objects, methods, nulls, base types
• C syntax
• Packages, imports, Javadoc, common libraries
• Inheritance, constructors
• Abstract classes, interfaces
• Event programming, callbacks, listeners
• Exception handling
• Class paths - java compilation
• Competent use of an IDE
• use of java in some context - eg database,
  ticketing application, game, client/server

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Parsing XML
TextArea
Orders
HTTP Post
Product
Person
lt?xml version 1.0?gt ltordersgt ltorderitem
personid235 gt ltproductgtchoc
lt/productgt ltqtygt535lt/qtygt
lt/orderitemgt lt/ordersgt
OrderItem
Address
Servlet
DB Connection
We program with objects Objects and Arrows But
XML is simply an ASCII file
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Class ExerciseHow to read in an XML file?
lt?xml version 1.0?gt ltordersgt ltorderitem
personid235 gt ltproductgtchoc
lt/productgt ltqtygt535lt/qtygt
lt/orderitemgt lt/ordersgt
Write some pseudo code to read the XML file and
turn it into an order object ? What are some
issues ?
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XML File
SAX or DOM
Lexical Tokeniser
Parser Grammar Checker
Internal Form
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Lexical scanning/parsing

• At base level - file is sequence of ascii
  characters
• Scanner (lexical) returns set of tokens and deals
  with whitespace
• (can it throw all the whitespace away?)
• Parser - checks the XML grammar
• (how many grammars are there?)
• startdocument
• lt?xml version1.0gt - Processing Instruction
• ltorderitemgt - Tag
• lt/orderitemgt - End Tag
• 545 - characters

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Processors

• XML has well developed processors for this task
• Take advantage of this work
• Months of development time plus wide use in
  market place
• Issues - new standards (eg what about schema)
• Complexities - CData, external entities,
  parameter entities, namespaces
• Recall why XML has taken off as data interchange
  format
• Because we already have processors and agreed
  syntax, we do not have to reinvent wheel of
  syntax, grammars and parsing of one-off formats !!

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XML Parsers

• XML Processors
• Parsers determine well-formedness of document
• Optionally determine validity
• Two common models
• SAX Simple API for XML
• DOM the Document Object Model

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DOM versus SAX
xml.fujitsu.com/en/tech/dom/
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SAX Parser

• SAX provides an event based interface to the
  parser.
• User callbacks are associated with events for
• startElement
• endElement
• characters (text)
• startDocument etc
• The callbacks are passed the data associated with
  the tag or the text of the character data.
• Good for large XML files - especially where
  processing required is linear.
• For us this is lower level - good place to start
  - however SAX requires much more programming than
  other XML processors

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Step 1 - Obtain Processor

• Apache Xerces http//xml.apache.org
• Others
• Sun Microsystems Crimson
• Microsofts MSXML Parser
• IBM XML4J
• Oracle XML Parser
• Check support of SAX 2.0, DOM Level 2
• To use Xerces with Java
• Download and unzip - eg C\xerces-1_4_3
• Include in CLASSPATH
• set CLASSPATH.c\xerces-1_4_3\xerces.jar

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http//java.sun.com/xml/jaxp/dist/1.1/docs/tutoria
l/sax/2a_echo.html
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Step 2 - UnderstandFramework
DefaultHandler
http//java.sun.com/xml/jaxp/dist/1.1/docs/tutoria
l/overview/3_apis.html
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SAX API Framework

• SaxParserFactory - creates instance of factory
• SaxParser - does the work, you pass it your
  DefaultHandler class
• DefaultHandler - wrapper for 4 classes below
• you extend this class and implement methods you
  require
• ContentHandler - interface - most of the work -
  methods such as startElement, endElement
• ErrorHandler - handles errors - 3 methods error,
  warning, fatalError
• DTDHandler - DTD entities, you probably wont need
• EntityResolver - resolve external entities, you
  probably wont need
• SAXReader - only if you want to get low level
  getXMLReader events

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Work Through Example

• We will work through an example from Sun
• This is a good tutorial for you to work through
  later, and is available online
• The code is detailed and intricate, you will need
  to study again at your leisure. However the
  tutorial covers many detailed aspects of the SAX
  API and is a valuable resource.
• Files - echo2.java, slideSample01.xml

http//java.sun.com/xml/jaxp/dist/1.1/docs/tutoria
l/sax/2a_echo.html
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Imports
import javax.xml.parsers.
import org.xml.sax.helpers.DefaultHandler
import org.xml.sax.
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Main Body
you extend DefaultHandler !
get instance of your class DefaultHandler
get instance of SAXParserFactory
then get the SAXParser
This does the Work handler calls itself
using callbacks
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Event Programming

• "An event driven program is just a bunch of
  objects laying around waiting for an event to
  happen."
• Do initial setup (register handlers)
• Start program
• Program waits for event to happen
• When event happens, event handler springs into
  action
• Program then waits for next event
• Some Java examples - WindowListener,
  ButtonHandler, SAX

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SAX Event Handlers

• startDocument()
• endDocument()
• startElement( String uri, String localname,
• String qname, Attributes atts)
• endElement(String name)
• characters (char ch, int start, int length)
• ignorableWhitespace(char ch, int start, int
  length)
• setDocumentLocator (Locator locator)
• uri - namespace URI
• localName - unprefixed name
• qname - with prefix eg oraelement

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Back to Echo Program
These methods are part of the Echo2 class
defined earlier
Recall line - saxParser.parse( new
File(argv0), handler) Registers this object
as the handler Then when events occur, call
thyself
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Echo Program
startElement
attrs.getLength()
attrs.getValue(i)
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Echo Program
endElement
characters
why StringBuffer ??
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Utilities
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Results of running ECHO2
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Document Locator

• public void setDocumentLocator(Locator loc)  
•  try     
• out.write("LOCATOR")
•     out.write("SYS ID " loc.getSystemId()
  )
•     out.flush()   
• catch (IOException e)     // Ignore
  errors   
• gtgt LOCATOR SYS ID fileltpathgt/../samples/slideSam
  ple01.xml
• Store locator so when callback occurs, you can
  have access to file information
• Must only be used within scope of the document
  parse

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try, catch, throws, exception

• Javas inbuilt mechanisms for when things go
  wrong
• can not convert a string to a number, sql errors,
  file IO
• an Exception object is generated - thrown
• your job is to catch exception
• statements that cause a problem are encased in a
  try statement
• SAX Errors - fatalError, error, warning

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Exceptions
try // statements that could cause a
problem catch (SaxException) // error
statements
Exception Methods getMessage() getLineNumber
() getSystemId ()
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SAX Exceptions

• warnings
• usually related to DTD, informative, eg element
  defined twice
• fatalError
• necessitates stopping parser - eg not well-formed
• error (Non Fatal error)
• related to DTD, validating error
• Default is to keep going - you may wish to
  override
• public void error(SaxParseException exc) throws
  SAXException
• System.out.println(Parsing Warning\n
  
• Line exc.getLineNumber() \n
  URI exc.getSystemId() \n
• Message exc.getMessage())
• throw new SAXException(Warning
  encountered)

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Introducing DTDs to XML

• If you introduce a DTD your parser will behave
  slightly differently

extra CHARS
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DTD Processing

• Without DTD whitespace is returned
• With DTD, whitespace can be ignored when element
  structure is known
• BUT YOU May wish to preserve or track white space
• eg to preserve document indenting
• Use method ignorableWhiteSpace
• public void ignorableWhitespace char buf, int
  offset, int Len)
• throws SAXException
•   nl()   
• emit("IGNORABLE")

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Validating Documents

• Validating Documents
• Schema or DTD must be present
• the ignorableWhitespace method is invoked
  whenever possible
• Note that a DTD is processed even if it is not
  validated
• To turn validation on, you must use the
  validation feature

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Using a Validating Parser
public static void main(String argv)   if
(argv.length ! 1)     ...      // Do not use
the default (non-validating) parser     // Use
the validating parser    SAXParserFactory
factory SAXParserFactory.newInstance()
  factory.setValidating(true)    try
    ...
see echo10.java
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Features

• A feature is a flag used by processor to indicate
  whether a certain type of processing should
  occur. eg in JAXP use
• factory.setNamespaceAware(true)
• factory.setValidating(true)
• Note that this is not related to the DTDHandler
  interface

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LexicalHandler

• Sometimes you may wish to preserve the original
  XML document as it is
• eg entities lt rather than lt
• comments
• CDATA
• There is an interface called LexicalHandler
• comment(String comment)Passes comments to the
  application.
• startCDATA(), endCDATA()Tells when a CDATA
  section is starting and ending, which tells your
  application what kind of characters to expect the
  next time characters() is called.
• startEntity(String name), endEntity(String
  name)Gives the name of a parsed entity. 
• startDTD(String name, String publicId, String
  systemId), endDTD()Tells when a DTD is being
  processed, and identifies it.

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JAXP

• JAXP - Java API For XML Processing
• makes it easier to process XML data
• Abstract Layer between program and SAX, DOM, XSL
• Provides namespace support
• The examples so far have used JAXP, which means
  imports and factory calls are easier
• Underneath, it still uses the DOM and SAX API

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Using SAX Without JAXP
import org.xml.sax.helpers.XMLReaderFactory impor
t org.xml.sax.XMLReader import
org.xml.sax.helpers.DefaultHandler import
org.w3c.doc.Document DefaultHandler
handler String filename XMLReader parser
XMLReaderFactory.createXMLReader() parser.setCont
entHandler(handler) // parser.setDTDHandler(handl
er) // parser.setErrorHandler(handler) parser.pa
rse(filename) // parser.setFeature(http//xml.o
rg/sax/features/namespaces, true) parser.setFeat
ure(http//xml.org/sax/features/validation,
true)
p57, Maruyama et al
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SAX 1 - Now Deprecated
Used to have to specify all methods in interface
documentHandler, HandlerBase, AttributeList,
XMLReader methods have been replaced by
equivalences in SAX 2.
http//developer.java.sun.com/developer/technicalA
rticles/xml/JavaTechandXML/
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SAX 1 - DocumentHandler
public class myXMLHandler implements
DocumentHandler public void
setDocumentLocator(Locator loc) public
void startDocument() public void
endDocument() public void
startElement (String tag, AttributeList atts)
public void endElement (String tag)
public void characters (char ch, int
start, int len) public void
ignorableWhiteSpace(char ch, int start, int
length) public void processingInstructi
on(String target, String data) and to
call XMLReader xmlReader
XMLReaderFactory.createXMLReader(PARSER_NAME) xml
Reader.setContentHandler (myXMLHandler) xmlReader
.parse ( filename.xml)
In SAX2 , this has been replaced by
ContentHandler or better still DefaultHandler
(an ADAPTER class)
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Notes

• Often StartElement and EndElement will end up
  doing a lot of the processing work
• You will end up with a set of nested case
  statements for each element type
• You may need something extra to keep track or
  where you are
• Consider using a Stack or a set of state
  constants

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Use of States
protected static final int ROOT 0, CATALOG 1
public void startElement(String uri,
String localName, String tag, Attributes atts)
if ( tag.equals(Catalog) state
ROOT) state CATALOG else if
(tag..equals(Product) state CATALOG)
state PRODUCT id
atts.getValue(id) text
null .. public void endElement(String uri,
String lname, String tag) if
(tag.equals(Catalog) state CATALOG
..
Marchal, p23 - 25
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Some Java References
Bradley, Millspaugh, Programming with Java
Bruce Eckel Thinking in Java
Horstmann Core Java
High Level Introduction
Online as PDF
Course notes http//www.comp.mq.edu.au/courses/com
p833/ password is comp833a http//www.comp.mq.edu
.au/courses/comp824/ password is comp824dis
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Java and XML References
McLaughlin Java XML, 2nd e
Benoit Marchal Applied XML Solutions
Maruyama et al XML and Java - Second Edition
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Java Documentation Online start using it !
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Tools

• Computer, Internet, monitor (windows/unix)
• Text Editor (Notepad, vi)
• Command/ms-dos window
• XML Tools
• Xerces
• Java Development Kit
• can be downloaded from Sun - also check out the
  Java Web Services Development kit
• IDE -
• Bluej is in labs - it is small with nice editor -
  can download from www.bluej.org for home use
• Netbeans - free and more sophisticated - includes
  servlets - www.netbean.org
• JBuilder - in labs - need to register to get key
• JDeveloper - in labs - can use for compilation -
  we cant change the library paths

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Example - Primitive Types
public class MyBasicVars ( public static void
main ( String args ) double pi
3.14 int j 1 boolean more true while (
more ) int jsquare j j System.out.print
ln ( Square is jsquare) j j 1 if
( j gt 10 ) more false
double varname int varname boolean varname
while (cond)
if (cond)