Ack, I forgot to mention this earlier...

There is a bug in the client when encoding odd unicode characters.
Try sending a @QueryParam with emoji chars. It's double-encoding the
% character.

I have a clear case in which a Resteasy method calls out to a remote
Resteasy method passing some parameters. I've tried to distill it
here.

This is the input URL to the first method, which works fine. I get a
String with the correct chars.

/my/url?msg=emoji+stuff+%EE%81%96%EE%90%8F

Calling a client method with that msg parameter produced a url that
looked more or less like this:

http://example.com/other/url?msg=emoji+stuff+%EE%2581%2596%EE%2590%258F

Note the double encoding of % to %25.

I'm currently falling back to constructing the outbound URLs by hand,
which works, so it's not a Java charset issue.