Costin Manolache wrote:
If I remember correctly ( and if it didn't change ), tomcat needs modeler in a parent classloader. Modeler has an optional dependency on digester, which depends on beanutils and collections. They both depend on logging, and modeler also depends on jmx.
So unless some classloader trick is used - we have to have collections in the parent loader - which forces the entire tomcat instalation to use the same collection version ( unless reverse loader tricks are used ).
That implies that if tomcat upgrades to collections3.0 - all webapps that use collections2.0 may stop working.
Why ? I don't understand. Tomcat will override anything except the system classloader.
You mean the classes in the common loader get overriden by the reverse loader ? Does it work if some classes are loaded with a loader ( for example some from the old package ) and some are loaded with the other loader ? I mean, can we force a loader for a particular package - blocking delegation completely ( even for classes that are not found ) ?
Even more interesting - we don't actually have this choice - since if digester changes to the new collections, we're forced to do the same :-)
What if we use modeler without digester ? Are there other components that depend on digester + collections ? At least for emebed this would be a good solution ( it won't reduce the size too much, but it may reduce the dependency impact it has when it's embeded - since whatever app it is emebeded into will be forced to update collections and all packages that depend on it - or do classloader tricks )
The startup code depends on digester :-( The web.xml parsing depends on digester. Etc, etc :-(
I think some of it can be done in a separate loader ( I tried it at some time ), at least loading the web.xml part. For the startup code - I don't know ( but it could use ant or jmx ).
I guess a lot has changed since I last looked, but packages like collections 3 in the top class loader makes me pretty uncomfortable.
( the real problem will be for apps that embed tomcat, when digester or other components will start using collection3 - forcing tomcat too ).
Costin
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