Howto print java class garbage collection events?

Question

java version \"1.5.0_14\"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_14-b03)
Java HotSpot(TM) Server VM (build 1.5.0_14-b03, mixed mode)

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Answer 1

It turns out that eclipse is the main issue here.

I'll explain:

I have wrapped our webapp in a main() method in order to test performance. We use a lot of 3rd party code, namely Apache commons-pool.

It turns out we had several versions of the jar spread across the projects (eclipse projects). My app which uses these projects had commons-pool-1.3, a different project had commons-pool-1.2.

When loaded using the servlet container (Tomcat6) the webapp class loader had first priority so it always loaded the webapp version. When I started the application using main() eclipse in it's not very wise behavior exported the depended projects jars in in the -classpath BEFORE the ones in the current project.

The conflict was between 2 versions of commons-pool, which caused a non defined behavior - On a object borrow is SOMETIMES decided to create a new object. I haven't looked inside the implementation code, I assume that this is something to do with a static map hold by the GenericKeyedObjectPool (the problematic class). Because a new instance was created it indeed contains a null reference to the mentioned global.

The solution to my luck was rather simple, commons-pool is being used only by my webapp so I could delete it from all referenced projects, otherwise I think i would just try to upgrade them all to a single version. If I couldn't do either I really don't know what would I've done. This is a very strange default of eclipse.

Thank you for reading and helping.

// ps. 3 days. That's the time I've spend on understanding what the hell I did wrong in my servlet replacement code. Turns out I'm not even the problem. :P