[jdom-interest] newbie question
bob at werken.com
Wed Dec 4 07:06:03 PST 2002
> I agree that XPath is probably not the fastest (CPU-wise) solution but why do
> you think XPath can lead to memory problems?
> The XPath engine allocates memory when it compiles the XPath expression (when
> you invoke XPath.newInstance) but not when evaluating the expression against a
> given node. At this stage, it just navigates the document.
> There's one exception to the above rule in Jaxen: Namespaces. When evaluating
> namespaces, the XPath engine allocates wrapper objects as XPath Namespaces do
> have a parent while JDOM's don't.
> As for speed, you can reach quite good performances by compiling XPath
> expressions and reusing them (i.e. using XPath.newInstance rather than the
> static selectNodes and selectSingleNode). If need be, you can use XPath
> variables in your expressions to use few generic compiled XPaths and call
> setVariable to "adapt" the expression before each evaluation.
Also, fwiw, I've got changes in the pipe-line, so that when evaluating
the XPath, you can pass a VariableContext into the method, allowing for
multi-threadsafe evaluation of an XPath with simultaneous different
variable bindings. Not in jaxen yet, but soon. Was just an oversight.
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