Spring is big and grows fast. It has quite some history, so it covers lots of things, lots of them are probably
not useful for your work. You do not have to use/learn everything. What is really powerful is the idea IoC. So
I would suggest to read about the basic IoC first and then proceeds to where really is pertinent to you.
Also, Spring's documentation turns to be only useful for reference instead of learning from scratch. So I would
suggest to find read books instead of their docs although they might be a bit out-of-date.
Some options:
Spring in Action: a little out-of-date, still about spring 2 as of now Mar, 2011, not much annotation, good for
the basics though.
Spring Recipes: A Problem-Solution Approach: more up-to-date spring 2.5. Fairly good after you know the
basic things in spring.
Rod Johnson's book: the inventer of spring. Good to understand the principle. But quite out-of-date in terms
of specific things.