SAX

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SAX

• A parser for XML Documents

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XML Parsers

• What is an XML parser?
• Software that reads and parses XML
• Passes data to the invoking application
• The application does something useful with the
  data

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XML Parsers

• Why is this a good thing?
• Since XML is a standard, we can write generic
  programs to parse XML data
• Frees the programmer from writing a new parser
  each time a new data format comes along

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XML Parsers

• Two types of parser
• SAX (Simple API for XML)
• Event driven API
• Sends events to the application as the document
  is read
• DOM (Document Object Model)
• Reads the entire document into memory in a tree
  structure

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Simple API for XML
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SAX Parser

• When should I use it?
• Large documents
• Memory constrained devices
• When should I use something else?
• If you need to modify the document
• SAX doesnt remember previous events unless you
  write explicit code to do so.

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SAX Parser

• Which languages are supported?
• Java
• Perl
• C
• Python

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SAX Parser

• Versions
• SAX 1 introduced in May 1998
• SAX 2.0 introduced in May 2000 and adds support
  for
• namespaces
• filter chains
• querying and setting properties in the parser

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SAX Parser

• Some popular SAX APIs
• Apache XML Project Xerces Java Parser
  http//xml.apache.org/xerces-j/index.html
• IBMs XML for Java (XML4J) http//www.alphaworks.i
  bm.com/formula/xml
• For a complete list, see http//www.megginson.com/
  SAX

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SAX Implementation in Java

• Create a class which extends the SAX event handler

Import org.xml.sax. import org.xml.sax.helpers.P
arserFactory Public class SaxApplication
extends HandlerBase public static void
main(String args)
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SAX Implementation in Java

• Create a SAX Parser

public static void main(args) String
parserName org.apache.xerces.parsers.SAXParser
try SaxApplication app new
SaxApplication() Parser parser
ParserFactory.makeParser(parserName) parser.set
DocumentHandler(app) parser.setErrorHandler(app
) parser.parse(new InputSource(args0))
catch (Throwable t) // Handle exceptions
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SAX Implementation in Java

• Override event handlers of interest

Public class SaxApplication extends HandlerBase
public void main (String args) // stuff
missing public void startElement(String
name, AttributeList attrs) // Process this
element
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SAX Implementation in Java

• Other events generated by the parser
• startDocument()
• endDocument()
• startElement()
• endElement()
• error()

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For more information...

• java.sun.com/xml
• www.megginson.com/SAX
• www.xml.com
• www.ibm.com/developer/xml