Re: DO NOT REPLY [Bug 16749] New: - Struts EL tag handlers cannot be reused by containers

["David M. Karr" <dm...@earthlink.net>]

I wanted to give a little status on this and query the committers on how they
would like me to proceed.

I've finished the changes for this, but I haven't checked anything in, as the
consensus was that we wanted to delay a fix for this until after 1.1.  The
change "simply" required making sure every attribute of every tag was
represented by an instance variable of the ELTag class (all suffixed with
"Expr"), along with associated getters and setters for each attribute.  The
BeanInfo class maps each plain attribute name to the "set<attr>Expr()" setter
method.

In the "evaluateExpressions()" methods, it calls "get<attr>Expr()" to get the
current expression value, evaluates the expression through the EL engine, and
calls "set<attr>()" on the result.

Although the number of lines changed and added represent a huge percentage of
the existing code, all of these changes were very straightforward.  So
straightforward that I performed most of the changes with an Emacs Elisp
script.

With this setup, even if the setter method associated with the attribute is
only called once (because the container saw it using a "static" value), the
correct value will be retrieved inside the "doStartTag()" call, to evaluate the
expression in the context of the reused tag.

Again, the fault with the previous code is that many of the getter methods
associated with the tag attributes were set to use the base class getter
method.  If the setter method wasn't called again to set the EL expression, the
value pulled out of the getter would be the evaluated value, not the
expression.  With this change, the expression string is preserved so it could
be used when the tag handler is reused.

I've run through my existing Cactus tests, and I've manually displayed all the
pages in the strutsel-exercise-taglib.  I have ONLY used Tomcat 4.1.10 and
4.1.18 for my testing, and neither the Cactus tests or the exercise taglib
tests every aspect of the library.  In fact, the Cactus tests don't test all of
the tags, and neither does the exercise taglib.  Nevertheless, based on my
understanding of the problem and the change I've made, I'm reasonably confident
this will work in Resin, or any other container that takes advantage of this
optimization defined in the JSP specification.  I don't know of any other
containers besides Resin that uses this optimization.  I asked about this on
one of the WebLogic newsgroups, but I haven't gotten a response yet.

Along the way, I discovered another problem that caused me to remove a line of
code from every expression evaluation.  When expressions are evaluated, if the
attribute expression was null, it causes a call to "set<attr>(null)".  This
caused problems in cases where an unset attribute in a base class has a
non-null default value (like the "name" attribute in several tags).  I fixed
this by removing the call to "set<attr>(null)" if the expression was null.  I
realized this could be more efficient, by just not evaluating it if the
expression was null.  I'll look at enhancing that in a later release.

Again, I've finished these changes and done some testing, but I don't have
Resin or other containers installed to test on any other containers.  I'd like
to make this fix available for the 1.1 release, but I admit there's some risk
involved.  Even worse, tomorrow morning (Sunday) I'm going out of town until
very late Friday evening.  I won't be able to check my email until somewhat
late on Saturday morning.

As a risk mitigation strategy, is it reasonable/practical to tag all the
current versions of the files in the struts-el directory with a label like
"BEFORE_ATTR_FIX"?  If I do commit these changes and they create unexpected
problems, "someone" might be able to back up the versions to that tag.

Also, if I do commit these changes, I'd like to know if someone, especially
including the person who reported the problem with Resin (perhaps unlikely on
Saturday), would be able to get the latest changes and run their test case, as
soon as possible, before the end of this day (say, 10pm PST).  As much as I'd
like to release this in 1.1 so containers using this optimization can use
Struts-EL effectively, I will not commit this today unless I get a good
response before this evening.

-- 
===================================================================
David M. Karr          ; Java/J2EE/XML/Unix/C++
dmkarr@earthlink.net   ; SCJP; SCWCD




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Re: DO NOT REPLY [Bug 16749] New: - Struts EL tag handlers cannot be reused by containers

[Mark Abbott <Ma...@openwave.com>]

Hi David - you are, of course, already out of town.
Sorry I could not respond earlier.  I can test with
a nightly build or even just a built struts-el.jar
and the tld files if they've changed, if this would
help you, once you return.

     Cheers - Mark

At 05:51 PM 2/8/2003, you wrote:
>Also, if I do commit these changes, I'd like to know if someone, especially
>including the person who reported the problem with Resin (perhaps unlikely on
>Saturday), would be able to get the latest changes and run their test case, as
>soon as possible, before the end of this day (say, 10pm PST).  As much as I'd
>like to release this in 1.1 so containers using this optimization can use
>Struts-EL effectively, I will not commit this today unless I get a good
>response before this evening.


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