Servlets 101, under Tomcat 6:

Could someone kindly point me to a good explanation of the best way to eg. create a Collection of expensive Foo objects at servlet startup time and stash them somewhere where I can access them while processing each request?

Near as I can tell there are at least three ways to do this and I am a bit fuzzy on the difference. I am not concerned with clustering or algorithms to evict stale entries or anything like that, just the basics.

Cheers and Thanks.