i completely DISAGREE with the recommendation above. this book has many examples for old struts version 1.0 mixing up with examples from v.1.1. the first few chapters are helpful in understanding struts, but that's about it.
i occasionally refer to the ted husted 'struts in action', but haven't done that for over a year. it also has the same problem with 1.0/1.1 mixing of examples. it does have a great chapter on tiles and the core classes of struts.
i had a glance through the table of contents, Struts: The Complete Reference (on amazon.com) seems to cover everything you'll need more practically. the book was published 04/2004 so it's much more up-to-date.
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As Alan suggested, Struts: The Complete Reference by James Holmes would certainly be suitable for a beginner. Since it's been updated with a second edition, O'Reilly's Programming Jakarta Struts by Chuck Cavaness might be worth checking out as well. It's slightly dated now, but I do still find value with Manning's Struts In Action by Ted Husted, which at one time at least had to be considered the definitive guide to Struts. The best intermediate/advanced level Struts book I've come across, and the one I find myself referencing most these days, is the second edition of Pro Jakarta Struts by John Carnell (APress).