The only way to achieve lemmatization today is to use the SynonymFilterFactory. The available stemmers are also inaccurate since they are only following simplistic rules.
A dictionary-based lemmatizer will be more precise because it has the opportunity to know the part of speech. Thus it provides a more precise method to stem words compared to other dictionary-based stemmers such as Hunspell.
This is my effort to develop such a lemmatizer for Apache Lucene. The documentation is temporarily placed here: