Have you searched the web for IoC and AOP? There are a *lot* of references to both.
In a nutshell, IoC allows an external force to determine what implementation will be used by code rather than the code determining the implementation. The "external force" might be a configuration file, a
unit test, other different code, etc.
AOP allows cross-cutting concerns to be implemented outside of the code affected by those concerns.
The "purpose" of Spring includes IoC and AOP, but goes quite a ways beyond that in its scope.
