Lucene - A high-performance, full-featured text search engine library

Lucene is most popular and java based searchengine library. It offers near real time search. Its features include Ranked search, many powerful query types: phrase queries, wildcard queries, proximity queries, range queries and more, fielded searching (e.g., title, author, contents), date-range searching, sorting by any field , multiple-index searching with merged results , allows simultaneous update and searching.