XOM API for Processing XML with Java

[Elliotte Harold <elharo AT metalab.unc.edu>]

peter murray-rust wrote:

> Personally as a user of XOM I would find it much easier if all 
> namespaces were easily available in all their descendant elements.

You can get a list of the namespaces in scope on an element using an 
XPath query such as

Nodes namespaces = element.query("namespace::node()");

This still ascends the tree, but at least you don't have to write your 
own code for doing so.

I've written a simple benchmark to see just how bad the various methods 
for iterating over namespaces really are.

https://xom.dev.java.net/source/browse/xom/src/nu/xom/benchmarks/NamespaceLister.java?rev=1.1&view=markup

I'm not finished yet, but so far I'm not sure there's a practical 
problem here. In my tests against http://www.rddl.org/ this code is able 
to retrieve each and every namespace URI, both in scope and declared, 
for every element in the document in between .1 and .3 seconds. No 
caching is done. i.e. each element is treated independently of the 
others. Thus the time to retrieve namespaces declared or in scope for 
just one element would be a small fraction of that.

I have not yet profiled this benchmark, so it's still possible that it's 
spending most of its time in something irrelevant like 
System.out.println(). However I think it does set a fairly low upper 
bound on the amount of time it takes to retrieve all namespaces declared 
or in scope, despite the aggressively suboptimal implementation.

There are definitely some optimizations I could make to 
getNamespacePrefix(int) and related methods. So far though it's not 
obvious this is worth doing. In practice, I suspect parsing, 
serializing, or simple I/O is likely to swamp any improvements I make in 
this method. Is anyone's code actually spending enough time here that 
this becomes the hot spot?

--
Elliotte Rusty Harold  elharo AT metalab.unc.edu
XML in a Nutshell 3rd Edition Just Published!
http://www.cafeconleche.org/books/xian3/
http://www.amazon.com/exec/obidos/ISBN=0596007647/cafeaulaitA/ref=nosim