Java and XML, Second Edition

Namespaces

An important addition to DOM Level 2 not yet discussed is DOM’s support for XML namespaces. You’ll remember from Chapter 3 and Chapter 4, that SAX 2.0 added namespace support, and the same is true for the second iteration of DOM. The key here is two new methods on the Node interface: getPrefix( ) and getNamespaceURI( ) . Additionally, all of the creation methods have namespace-aware versions available. So, instead of calling createElement( ), you call createElementNS( ).

Overloaded?

To all of the Java programmers out there, createElementNS( ) looks pretty odd. Why not just overload createElement( ) to take in additional parameters? Well, you could if DOM was used only in Java or in languages that supported overloading. However, it’s not; it’s a cross-language specification, and that results in limitations with method names and backwards compatiblity when it comes to changing existing method signatures. So, DOM defined new methods with the NS suffix to identify them as namespace-aware versions. It’s bad for straight Java, but good for DOM as a cross-language standard.

In each of these new namespace-aware methods, the first argument is the namespace URI, and the second is the qualified name of the element, attribute, etc. Note that I said qualified; this means that if you want to use a namespace URI of “http://www.oreilly.com” and a prefix of “ora” on an element called “copyright”, you would call createElementNS("http://www.oreilly.com", "ora:copyright"). This is very ...