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From rmenon <rmenon...@gmail.com>
Subject Re: Digester 1.8 classloader issue when using tomcat
Date Sun, 04 Jan 2009 15:47:31 GMT

Thank you
Now I understand what Rahul meant by "portable".  Chances of our changing
web servers is slim.

Well, if I had not used digester, I could have put the common war file in
the shared/lib.  I am ok with not sharing digester itself but the fact that
all the digester constructed classes need to be put in WEB-INF/lib seems to
be a severe restriction to me. 
By the way, has anyone done an analysis of how much it costs to duplicate
the war files in terms of memory?

Thanx again for the reply to you and Rahul.

Menon

jwcarman wrote:
> 
> BeanUtils (which Digester uses) uses static variables, so sharing that
> particular stuff across webapps can cause some trouble.  As Rahul
> said, just put the stuff in your WEB-INF/lib directory.  It's more
> portable that way (you can just plop your war file down in any other
> web server if it's constructed this way).
> 
> On Sat, Jan 3, 2009 at 5:27 PM, rmenon <rmenon.us@gmail.com> wrote:
>>
>>
>>
>> Rahul Akolkar wrote:
>>>
>>> On Sat, Jan 3, 2009 at 3:51 PM, rmenon <rmenon.us@gmail.com> wrote:
>>>>
>>>> Well,
>>>> Can you please elaborate a bit more? My question is why should we
>>>> reload
>>>> the
>>>> same classes multiple times for a jar file that is shared by multiple
>>>> web
>>>> apps?
>>> <snip/>
>>>
>>> Generally you want your apps to be self-contained. The servlet
>>> specification talks about the web app and its directory structure,
>>> shared stuff is often container specific (I did mention portability).
>>>
>>>
>>> Well, from what I understand, at least in tomcat (which is what we use),
>>> there is a shared/lib
>>> directory for jars that are common across applications. These jars need
>>> not be container specific.
>>>
>>>
>>> And I am not sure what you mean portability? Could you explain a bit
>>> more?
>>>
>>>> Also, if I do not use digester, then this is not an issue - so what
>>>> are people who use digester doing (apart from duplicating war files)?
>>> <snap/>
>>>
>>> I think you mean duplicating libraries in war files for different web
>>> apps with similar application dependencies.
>>>
>>> I meant duplicating a jar file that is shared across applications in
>>> each
>>> of the applications's WEB-INF/lib
>>> directories. I would think that there should be a way to put them in
>>> shared/lib directory and still be able to use digester to construct
>>> them.
>>>
>>>
>>>> I do
>>>> not like the idea of duplicating same war files for each web app - so
>>>> is
>>>> there a good reason to do that (apart from being a workaround for
>>>> problems
>>>> with digester.)
>>>>
>>> <snap/>
>>>
>>> I still think you mean adding the same jars to each WEB-INF/lib -- its
>>> portable and its safe.
>>>
>>> -Rahul
>>>
>>>
>>>>
>>>>
>>>> Rahul Akolkar wrote:
>>>>>
>>>>> On Sat, Jan 3, 2009 at 3:44 PM, rmenon <rmenon.us@gmail.com> wrote:
>>>>>>
>>>>>> Can you please elaborate? Are you suggesting that I should just
>>>>>> package
>>>>>> all
>>>>>> three jar files in WEB-INF/lib?
>>>>>>
>>>>> <snip/>
>>>>>
>>>>> If they are needed by the said web app, yes.
>>>>>
>>>>> -Rahul
>>>>>
>>>>>
>>>>>> Rahul Akolkar wrote:
>>>>>>>
>>>>>>> On Sat, Jan 3, 2009 at 2:14 PM, rmenon <rmenon.us@gmail.com>
wrote:
>>>>>>>>
>>>>>>>> Hi
>>>>>>>> I have three jar files: common, webapp-common, my-webapp.jar.
>>>>>>>> common- can be used by non web apps
>>>>>>>> webapp-common - common stuff shared by web apps.
>>>>>>>> my-webapp.jar - a particular web app.
>>>>>>>>
>>>>>>>>  I am using digester to build my classes for the app my-webapp.jar.
>>>>>>>> In
>>>>>>>> the
>>>>>>>> digester rules, I have classes that are in all three jar
files.
>>>>>>>> Now,
>>>>>>>> ideally
>>>>>>>> speaking, I should be able to put the webapp-cmmon and common
jar
>>>>>>>> files
>>>>>>>> in
>>>>>>>> the shared/lib and the my-webapp.jar in WEB-INF/lib. However,
that
>>>>>>>> results
>>>>>>>> in the digester failing with "NoClassDefFoundException".
The
>>>>>>>> problem
>>>>>>>> goes
>>>>>>>> away if we put all three jars in the WEB-INF/lib since the
digester
>>>>>>>> class
>>>>>>>> loader can see those classes. However, the common jar is
already in
>>>>>>>> the
>>>>>>>> shared/lib being used by other apps. I added some new "common"
>>>>>>>> stuff
>>>>>>>> for
>>>>>>>> the
>>>>>>>> my-webapp.jar and hence running into this issue.
>>>>>>>>
>>>>>>>> My latest thinking is to separate out the portion of the
classes
>>>>>>>> being
>>>>>>>> used
>>>>>>>> by the my-webapp.jar from the common jar file into its own
jar.
>>>>>>>> Then
>>>>>>>> I
>>>>>>>> can
>>>>>>>> bundle the webapp-common ahd my-webapp.jar in to the WEBINF/lib
and
>>>>>>>> retain
>>>>>>>> the common jar in the shared/lib. Is there a better approach?
What
>>>>>>>> is
>>>>>>>> the
>>>>>>>> best practice in this scenario. Does someone have an idea
of
>>>>>>>> overhead
>>>>>>>> in
>>>>>>>> terms of performance etc if we "duplicate" jar files in each
app
>>>>>>>> instead
>>>>>>>> of
>>>>>>>> sharing them in common/lib? What I do not like about this
issue is
>>>>>>>> that
>>>>>>>> I
>>>>>>>> think this issue would not be there if I was creating objects
>>>>>>>> without
>>>>>>>> using
>>>>>>>> digester - so a way to use the approach (where I can access
the
>>>>>>>> common
>>>>>>>> classes from digester) would be really ideal in my opinion.
>>>>>>>>
>>>>>>>> I did search the google and also this forum - I note that
someone
>>>>>>>> suggested
>>>>>>>> to always bundle each jar files within the web app itself
>>>>>>>> separately.
>>>>>>>> What
>>>>>>>> is the rationale for that?
>>>>>>>>
>>>>>>> <snip/>
>>>>>>>
>>>>>>> Portability, potential trouble with statics etc. Also, digester
>>>>>>> itself
>>>>>>> (and beanutils in particular) should never be shared.
>>>>>>>
>>>>>>> -Rahul
>>>>>>>
>>>
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>>>
>>
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