Am I wrong or most of the answers are beside the point?
To answer precisely your question, yes, you can submit a comma separated list to a POST parameter. To be honest, I just did a quick try with a PHP script, but I don't see why Java would behave differently. One point with POST requests is precisely that you have much less constraints on syntax (no need to escape = & or such).
So if you explain more in details what "doesn't work", perhaps we can help you more.
