XOM API for Processing XML with Java

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

At 7:07 AM -0400 9/4/04, Elliotte Rusty Harold wrote:

> Last night I realized another reason to deprecate and eliminate the 
> last four of these constructors. Each one of them creates anew 
> Builder object. This is potentially quite an expensive operation. 
> Whether it's expensive relative to compiling the stylesheet and 
> running the transform depends on local circumstances, but in at 
> least some circumstances it makes a lot more sense to reuse a 
> builder if possible, rather than creating a new underlying XMLReader 
> for each separate document.

And now that I've looked at the code rather than relying on my faulty 
imaginings of how this class works, I'm realizing I was 100% wrong. 
In fact I may have this all exactly backwards.

The XSLTransform constructor does not call new Builder(). Instead it 
just passes the Reader/InputStream/File/URL straight into TrAX which 
does whatever it does with it (presumably including parsing the 
stylesheet.) That still might involve loading an XMLReader. However, 
creating a Document object with a Builder does not avoid this problem!

When a Document object is passed to an XSLTransform constructor it is 
written  into a StringBuffer which is then passed to TrAX as a 
StringReader. Thus it gets parsed twice. In any case, it is more 
efficient just to pass in the Reader/InputStream/File/URL rather than 
a Document.

Now that I look at this I recall it was a quick hack to get something 
working, that I always intended to revisit and fix later. Perhaps 
later is now. I need to explore this further, and see if there's some 
way I can eliminate the reserialization and double parse from the 
XSLTransform(Document) constructor.

In the meantime, I don't want to deprecate the File and URL 
constructors since they are noticeably better than the Document 
constructor. I do still want to deprecate the InputStream and Reader 
constructors for the initial reasons cited earlier (they don't allow 
relative URLs to be resolved) but I think I should replace them with 
ones that add a second argument for the base URL.

Anyway, that's what I'm thinking now. If I can figure out how to 
avoid the double parse in the XSLTransform(Document) constructor I 
may change this again; but at least two of the constructors are 
sticking around for the time being.
--

  Elliotte Rusty Harold
  elharo AT metalab.unc.edu
  Effective XML (Addison-Wesley, 2003)
  http://www.cafeconleche.org/books/effectivexml
  http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/cafeaulaitA