Book for Spring

I have never used or learn about spring framework. i only know jsp and servlet (read from HFSJ) . Now i am involved in a project that uses spring framwork.
I would like to learn about this framework by referring any book.
Would any one of you suggest me a good book ?
Is there a Head first for it?

Spring In Action is good, and easy to follow. The third edition (Spring 3.0) is under way, but it may take some time until getting published. Some chapters are already available (pdf) if you buy it via Manning's MEAP. If you do, you'll also get the full Second Edition (Spring 2.5).

The Spring docs from the Spring Source website are a great source of reference!