Collection of useful codec, postings format and terms dictionary implementations.
Packages 
Package Description
org.apache.lucene.codecs.blockterms
Pluggable term index / block terms dictionary implementations.
org.apache.lucene.codecs.blocktreeords
Same postings format as Lucene50, except the terms dictionary also supports ords, i.e.
org.apache.lucene.codecs.bloom
Codec PostingsFormat for fast access to low-frequency terms such as primary key fields.
org.apache.lucene.codecs.memory
Term dictionary, DocValues or Postings formats that are read entirely into memory.
org.apache.lucene.codecs.simpletext
Simpletext Codec: writes human readable postings.