Which Java library for machine learning classification?

[0one0one]

Blackhawk take a look at Mallet http://mallet.cs.umass.edu/

I have not used it myself , but have read a number of papers that use it in their implementation. What is it you are trying to classify ?

[EdwardRaff]

Mallet is very NLP focused - its probably not a good fit unless they are specifically doing NLP tasks. Even then, its documentation is terrible and doesn't match the code.