Lucene 4.7.2 facet API

Provides faceted indexing and search capabilities.

See:
Description

Packages

org.apache.lucene.facet	faceted search
org.apache.lucene.facet.range	Provides range faceting capabilities.
org.apache.lucene.facet.sortedset	Provides faceting capabilities over facets that were indexed with SortedSetDocValuesFacetField.
org.apache.lucene.facet.taxonomy	Taxonomy of Categories
org.apache.lucene.facet.taxonomy.directory	Taxonomy index implementation using on top of a Directory.
org.apache.lucene.facet.taxonomy.writercache	Improves indexing time by caching a map of CategoryPath to their Ordinal.

Provides faceted indexing and search capabilities. Checkout this and this blog posts for some overview on the facets module as well as source code examples here.