XQJ (JSR 225)

[Michael Kay]

>   BTW, does someone knows why there is a difference between 
> an "expression" object that is actually used to evaluate 
> (possibly several different if I am right) XQuery expressions 
> and a "prepared expression" that really represents a 
> (compiled) XQuery expression?
> 
>   At first glance, it seems rather confusing to me.


It's a very strange design. It's worth noting that neither XQExpression nor
XQPreparedExpression is thread-safe - both extend XQDynamicContext and
therefore hold context information which is different for each evaluation of
the expression.

The difference between them is that XQPreparedExpression contains a compiled
expression or query, whereas XQExpression merely holds the dynamic context
for executing an expression or query - despite its name, the expression to
be evaluated is not held in the XQExpression object, but is always supplied
dynamically. 

Whenever I complained about the design (or even the nomenclature) I was told
it would all seem completely intuitive to people who know JDBC. I've no idea
whether that's true; I'm quite sure it's not a good justification.

Unless you need the portability, I recommend Saxon's s9api interface. It's
also probably more efficient. A weird consequence of the close() mechanism
in XQJ, which was presumably designed to allow resources to be released
early, is that Saxon has to maintain links between a connection and all the
objects created under that connection, and this stops those resources being
garbage collected.

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay