Beginning Web Development With Perl : From Novice to ... - Nabo

CHAPTER 9 ■ XML PARSING WITH PERL 179dob = 3/10email = frank@example.comvehicle = Volvo S60vehicle = Honda Accordrequired = emailcustomer =first_name = Sandylast_name = Sanbeansdob = 4/15email = sandy@example.comvehicle = McLaren MP4-20vehicle = Chevrolet S-10You’ve now seen how to parse XML using XML::SAX by creating your own handler for XML::SAXparser events. However, the examples here have only scratched the surface of XML parsing withXML::SAX. It is a very powerful specification and package with Perl. I invite you to spend some timereading the XML::SAX and XML::SAX::Base documentation and experimenting with the code andwith more complex examples to parse XML in Perl with this excellent module.Using Tree-Based ParsingThe chapter began with a look at XML::Simple for parsing simple XML. You then read aboutparsing of XML with XML::SAX, a framework around which very complex XML parsing can bedone. Tree-based parsing, or simply tree parsing, is yet another process for parsing XML. Thismethod delivers the entire XML structure to your program as one logical entity, as opposed tothe delivery in chunks that you get with a stream processor. As noted earlier in the chapter,tree parsers are almost always stream-based parsers at heart, but they hold the data until theend of the parsing.Needing to pass the entire structure at once almost always means that tree parsers havehigher memory requirements than their stream-based counterparts. Since XML structurescan be quite complex, it’s not uncommon to receive an Out of Memory error when usinga tree parser on complex and/or lengthy XML.Tree parsers include XML::Parser, which can be used both as a tree and a stream parser,XML::Grove, XML::TreeBuilder, XML::Twig, and XML::SimpleObject, just to name a few. Theparser that you saw earlier in the chapter, XML::Simple, is yet another tree parser.Each XML parser has its own features and invariably its own syntax as well. XML::Twig, forexample, is interesting in that it can hold part of the XML tree, thus saving memory. XML::Twigalso provides a simple means for converting XML into HTML or into other formats. The followingexample prints XML using the indented option with XML::Twig:#!/usr/bin/perluse strict;use XML::Twig;