Plucene is a fully-featured and highly customizable search engine toolkit based on the lucene api. (http://jakarta.apache.org/lucene)

it is not, in and of itself, a functional search engine - you are expected to subclass and tie all the pieces together to suit your own needs. the synopsis above gives a rough indication of how to use the engine in simple cases. see plucene::simple for one example of tying it all together.