Java and XML, Second Edition

Filters and Writers

At this point, I want to diverge from the beaten path. So far, I’ve detailed everything that’s in a “standard” SAX application, from the reader to the callbacks to the handlers. However, there are a lot of additional features in SAX that can really turn you into a power developer, and take you beyond the confines of “standard” SAX. In this section, I’ll introduce you to two of these: SAX filters and writers. Using classes both in the standard SAX distribution and available separately from the SAX web site (http://www.megginson.com/SAX), you can add some fairly advanced behavior to your SAX applications. This will also get you in the mindset of using SAX as a pipeline of events, rather than a single layer of processing. I’ll explain this concept in more detail, but suffice it to say that it really is the key to writing efficient and modular SAX code.

XMLFilters

First on the list is a class that comes in the basic SAX download from David Megginson’s site, and should be included with any parser distribution supporting SAX 2.0. The class in question here is org.xml.sax.XMLFilter. This class extends the XMLReader interface, and adds two new methods to that class:

public void setParent(XMLReader parent);

public XMLReader getParent( );

It might not seem like there is much to say here; what’s the big deal, right? Well, by allowing a hierarchy of XMLReader s through this filtering mechanism, you can build up a processing chain, or pipeline , of events. To understand ...