SAX2

Producer-Side Validation

All uses of SAX2 parsers will involve extending and customizing the basic scenario we saw earlier. Our next example illustrates two basic configuration mechanisms: error handling options, which lets you use the appropriate policy when you see errors, and parser configuration through feature flags, which let you control some details of how the parser works. (Some event handlers are managed with a configuration mechanism that is quite similar to the feature flag mechanism.) The example also shows how SAX2 parsers expose the core XML notion of DTD-based validation.

Validity and XML

Validation is particularly important when you are interchanging documents that have been wholly or partially authored by hand, but it can also be helpful when working with XML that’s generated by custom code. When you validate an XML document, you ensure that it meets certain rules needed to process them—such as requiring a title element as the first child of every chapter element or prohibiting dangling internal cross-references.

Validation is done at several levels in most applications. Lower levels tend to use rule-based logic, such as the DTD validation that’s defined by XML 1.0. The various types of XML schema provide different kinds of rule-based sanity checks, which are usually done before applications see the data. (W3C’s schemas also extract additional information items, beyond the XML data model of elements, attributes, and text. This information is called ...