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From "James Carman" <ja...@carmanconsulting.com>
Subject Re: Digester 1.8 classloader issue when using tomcat
Date Sun, 04 Jan 2009 03:02:38 GMT
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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