The most seamless solution would be Sphinx4 with JRuby. But I would 
recommend using pocketsphinx and calling it via command line, I found 
that it performs better and is much easier to use. Just use one of the 
acoustic models that come with pocketsphinx, write a JSGF grammar, 
generate a dictionary and you're good to go. As long as you have a 
limited grammar and a reasonably clear audio signal it's no rocket 
science to build something that works well.

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