SAX

Introdcution

SAX(unlike DOM)is not a W3C Recommendation.It is a public domain software,created by members of the XML-DEV mailing list, led by David Megginson. It is important to realize that SAX is an API,providing interfaces for parsers to implement.Therefore,SAX by itself can not be used to parse documents.

SAX  versus DOM

SAX  parsers process the XML document sequentially while DOM parsers load the entire document into memory store it in a tree structure.Therefore, SAX versus DOM, in other words, is the tradeoff:performance versus easy programming.(the different of  these parsers process between SAX and DOM is not mentioned detailedly.)

Understand SAX and Apply SAX(with Java)

SAX gives you access to the information in your XML document,not as a tree of nodes,but as a sequence of events.All that the parser does is to read through the XML document and fire some events depending on the tags encountered.

Then apply SAX in programing must follow following steps:

1. Create an event handler

2. Create a SAX parser

3. Assign event handler to SAX parser

4. Parse documet and send events to handler

1.Create an event handler

you must create a handler before application use the SAX to parse XML document. SAX provide a class called DefaultHandler, you can extend this class, and override the methods.

DefaultHandler is in package org.xml.sax.helpers.It implements ContentHandler,DTDHandler,EntityHandler and ErrorHandler.To use this class is imprtant to your application.

2.Create a SAX parser

there are 3 approachs to create a SAX parser. Invoke the driver directly, Specify the driver when run application  and Tranfer driver as a argument of the createXMLreader()

Invoke the driver directly can like this:

try {

      XMLReader xmlReader= new org.apache.xerces.parsers.SAXparser();

} cache (Exception e) {

     system.out.println("can't create the parser" + e.getMessage())

}

note: suppose that use the xerces parser.

Specify the driver when run application use command line to tranfer the driver to application.It's not good way, I think.

The last approach is wide used.

 

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