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From David Jencks <>
Subject Re: An idea for defining custom valves in config.xml
Date Mon, 06 Oct 2008 15:56:20 GMT

On Oct 6, 2008, at 7:22 AM, Jason Warner wrote:

> On Fri, Oct 3, 2008 at 6:55 PM, David Jencks  
> <> wrote:
> On Oct 3, 2008, at 12:51 PM, Jason Warner wrote:
>>   Hey all.  I'm working on an idea for allowing custom valves to be  
>> defined in config.xml.  Currently this isn't possible since the  
>> tomcat classloader would not contain the custom classes for the  
>> valve.  I've create a jira for tracking this issue [1] and it  
>> contains a few links to workarounds.  IMHO, The solution we should  
>> be looking for is a way to add classes to a module without having  
>> to undeploy, modify the module config, and redeploying.
> People have suggested stuff like this before.  IMO it pretty much  
> goes against the fundamental idea of geronimo of having fairly fixed  
> plugins with only a few knobs to turn to adjust things in config.xml  
> and
> Why is changing the classloader contents in config.xml a good idea?   
> What is so hard about redeploying the app if you want to change its  
> classloader significantly?  If you want to change a class in the app  
> you have to redeploy it.... why is this situation different?
> The specific instance I have in mind for this change is using a  
> custom valve for tomcat, so I think the scope really should be  
> limited to just the tomcat module.  I can't think of another  
> instance where this would be useful, so it's probably not necessary  
> or desirable to expand it further.  I believe this situation is  
> different because the structure of geronimo is causing a disconnect  
> between the functionality of tomcat and the functionality of tomcat  
> as it is embedded in geronimo.  As Don just said in the middle of my  
> typing this, I don't believe we should expect the average user to  
> have to rebuild one of our modules to add something that can be  
> added in a much simpler way within tomcat itself.

Could you explain more about the circumstances for this custom valve?   
Is it intended to be for every app deployed on this tomcat server  
instance rather than for one particular app?  Will it work if it is in  
a child classloader of the tomcat plugin classloader?

At the moment I would MUCH rather see us make it easier for users to  
deploy new/different/modified tomcat servers (and other plugins) than  
introduce a hack to modify classloaders of existing plugins.  Our  
customization story is already  too complicated, IMO we don't need to  
glue on more bits that don't actually fit well.

IMO the best end result for users is to have a new tomcat plugin with  
the needed extra jars and valve configuration.  Lets look for a way to  
make it really easy for our users to get there.

How would you deal with this in an osgi or spring environment?

david jencks
> Thanks!
> thanks
> david jencks
>> I think this can be done by allowing a user to indicate jars that  
>> should be loaded by a module within the config.xml.  These jars can  
>> then be added to the module's classloader for use by the module.   
>> I'm not extremely familiar with how our classloader works, but I've  
>> taken a look through the code and I think the ability to add to the  
>> classloader can be implemented without too much difficulty.  I'm  
>> not quite sure what type of scope to give this change, though.   
>> Should I leave it as a change aimed solely at tomcat valves or  
>> should it be expanded to encompass any configuration?  I realize  
>> this is only a rough idea of what i plan to do, but I'm still  
>> working out the details of how to proceed.  I'm hoping for some  
>> feedback on what I intend to do and possibly some alternate ideas  
>> if anyone has some.
>> Thanks!
>> [1]
>> -- 
>> ~Jason Warner
> -- 
> ~Jason Warner

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