This is going to give you different results with non-ASCII on Windows and on Linux. Actually on Windows you might get different results based on the locale.

I looked a bit at the REST server code and I don't really like the charset handling... we're just getting the Content-Type header field and sending it back to the client the way we got it. If the PUT request includes a charset in the content-type, and another client requests a different charset via Accept-Charset, we still reply with the original charset.

What's worse, the Content-Type header isn't even relevant for POST parameters, because they can have their own content-type in multipart/form-data encoding.

Anyway, I'll create a separate issue in JIRA for the POST handling, but we really should have a test for RestCodec with non-ASCII characters.