SAX A parser for XML Documents XML Parsers

XML Parsers • What is an XML parser? – Software that reads and parses

XML Parsers • Why is this a good thing? – Since XML is a

XML Parsers • Two types of parser – SAX (Simple API for XML) •

SAX Parser • When should I use it? – Large documents – Memory constrained

SAX Parser • Which languages are supported? – Java – Perl – C++ –

SAX Parser • Versions – SAX 1 introduced in May 1998 – SAX 2.

SAX Parser • Some popular SAX APIs – Apache XML Project Xerces Java Parser

SAX Implementation in Java • Create a class which extends the SAX event handler

SAX Implementation in Java • Create a SAX Parser public static void main(args[]) {

SAX Implementation in Java • Override event handlers of interest Public class Sax. Application

SAX Implementation in Java • Other events generated by the parser – start. Document()

For more information. . . • • java. sun. com/xml www. megginson. com/SAX www.

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SAX A parser for XML Documents

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

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

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

Simple API for XML

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 doesn’t remember previous events unless you write explicit code to do so.

SAX Parser • Which languages are supported? – Java – Perl – C++ – Python

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

SAX Parser • Some popular SAX APIs – Apache XML Project Xerces Java Parser http: //xml. apache. org/xerces-j/index. html – IBM’s XML for Java (XML 4 J) http: //www. alphaworks. ibm. com/formula/xml – For a complete list, see http: //www. megginson. com/SAX

SAX Implementation in Java • Create a class which extends the SAX event handler Import org. xml. sax. *; import org. xml. sax. helpers. Parser. Factory; Public class Sax. Application extends Handler. Base { public static void main(String args[]) { } }

SAX Implementation in Java • Create a SAX Parser public static void main(args[]) { String parser. Name = “org. apache. xerces. parsers. SAXParser”; try { Sax. Application app = new Sax. Application(); Parser parser = Parser. Factory. make. Parser(parser. Name); parser. set. Document. Handler(app); parser. set. Error. Handler(app); parser. parse(new Input. Source(args[0])); } catch (Throwable t) { // Handle exceptions } }

SAX Implementation in Java • Override event handlers of interest Public class Sax. Application extends Handler. Base { public void main (String args[]) { // stuff missing } public void start. Element(String name, Attribute. List attrs) { // Process this element } }

SAX Implementation in Java • Other events generated by the parser – start. Document() – end. Document() – start. Element() – end. Element() – error()

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