migrating a large-scale, poorly structured Java system to Spring application framework

i'm looking for development stories/experiences on migrating a Java system to Spring Application Framework. our aim is the benefits of a bean container and the dependency injection of Spring. We're not considering Spring MVC or any other of its specific components at the time.

Our system is currently using no bean container of any kind. all in pure Java-- nothing of JEE either. It has its own, house-built service engines for managing Db services, in-memory caches, session mngt, configuration, and certain product-specific components. what's more, it is purely structured. very poorly encapsulated -- needs lots of refactoring, elimination of duplicate and unused code, bug fixing. a good amount of our development efforts are going into bug-fixing rather than structural -- making it even more deteriorate. it's a 10+ year-old system and has been built around its original architecture.

we aren't even sure yet whether to work on its existing structure first then look to get the benefits of Spring, or to do them both at once.

to me, working a new architecture from scratch on Spring that implements the logic-- not the structure of the current system is the best. however, this may/not be as feasible since it won't have tangible results in a near-enough future for the upper management.

i'll appreciate direct/indirect references opinions, experiences and other input.

TIA.

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EDIT:

so - in a phrase, this is on "how to migrate a dinosaur to Spring ". it's a matter of strategy-- not of technical migration like how/where to organize/define/integrate the specific components.