Lucene in Action, by Michael McCandless, et al

This is a terrific guide book to the Lucene open source high-performance search engine.    One of the things I like most about it is how pragmatic it is:   for example, want to know how to write custom collectors -- and why?  There's an excellent explanation and helpful example code.

My only dissatisfaction is that I lack the spare time to play more with Lucene and try out some queries on my own.