xml2j
XML Schema SAX based code generator for Java
...With XSD there are many different possible approaches to defining a schema for your XML, therefore the generator first normalizes the XSD to an XML fit for code generation. The last step is the actual code genaration during which Java code is generated that extends the core framework.
A great asset is that the framework uses eventing allowing your application to subscribe to high-level events that correspond to your complexTypes. This is done using a properties file.
You have full control of memory usage making it a great fit for processing very large documents.