Apache Lucene
- Search engine library with many features including fast indexing, ranked searching, boolean, phrase, and span queries, date-range searching, and extension APIs. [Open Source]
- http://lucene.apache.org/java/docs/

OSSearch
- Servlet acting as a search engine for small websites. [Open Source]
- http://javaboutique.internet.com/servlets/OSSearch/

EGOTHOR
- A full-featured text search engine. Including starting guide, mailing list signup, and API documentation. [Open source, BSD-like]
- http://www.egothor.org/

SearchBlox
- A search application designed on a robust Java architecture. Results are delivered in a fast and relevant manner. SearchBlox is deployable on any Servlet 2.3/JSP 1.2 compliant server. [Commercial]
- http://www.searchblox.com/

eSearch
- Supplies basic search capabilities for Web use. [Open Source, BSD-like]
- http://www.jcorporate.com/econtent/Content.do;jsessionid=aaa7LxxireKymd19UfOg?state=template&template=2&db=default&resource=641

Java Search Engine
- Full featured text search engine for web sites, completely in Java. Can be easy integrated into any web site. Supports XML, XSLT, EJB. [Freeware]
- http://www.me.lv/jse/