NLP4L is a natural language processing tool for Apache Lucene written in Scala. The main objective of this OSS project is to use NLP technologies to improve Lucene users' search experience. The unique difference between NLP4L and other NLP tools is that NLP4L itself references Lucene index instead of raw text as its processing target. The session will describe how to use Scala to obtain word statistics and N-gram statistics from Lucene index and introduces various tools including the Hidden Markov model that are developed using these functions.