In this seminal article Fowler, apart, from explaining the concept lucidly also keeps up with his habit of rechristening, this is a good case at that where he uses the term Dependency Injection to better explain IoC.
Another optional article which may be of help to you is Robert Martin's DIP explanation:
Pro Spring 2.5 and Spring in action are two good books for Spring.
If you are looking for a fast and friendly read that gives you details as well as gets you off the ground fast then Spring in Action is the one. However, if you are looking for a terse(read as meatier) text then Pro Spring is the book for you. Pro Spring does a better job of explaining the concepts. If you are looking at one book and if time's on your side I would recommend Pro Spring, otherwise its SIA.
Look into the table of contents if breadth is of concern, both cover a lot of ground however each skips one or two topics which the other covers. For ex: Spring in Action covers Security which Pro Spring doesn't.
These should do for your initial exploration of Spring, read on for further resources and confusion. Probably the second stage if I may call it.
Spring Recipes is another great resource which you may take up after you are done with either of the earlier recommendations. That is my opinion however some may argue it could be a good start as well. The documentation for Spring is excellent, the reference manual lives up to its name of being so. Use the manual as a reference text either while learning Spring or after it, don't bother during your initial stages.
Apart from articles and books another great way of learning is participating in the forums. By reading the forums/ answering questions(even whose answers you don't know in entirety) you get to learn a lot that is not there in any of the books.