Error during WebSocket handshake: Unexpected response code

[CLEMENT Jean-Philippe]

Dear CXF experts,

I'm trying to connect a web client to a CXF WebSocket. The browser logs the 
error "WebSocket connection failed: Error during WebSocket handshake: 
Unexpected response code: XXX". The XXX response code changes depending on the 
@Produces annotation: 200 when text/plain, 406 when text/*.

The server Java looks like this:
@GET
@Path("monitor")
@Produces("text/*")
public StreamingOutput greetMonitor() {
 return stream -> {
  stream.write("Ok".getBytes());
  stream.flush();
 };
}

The client Javascript looks like this:
var socket= new 
WebSocket("ws://myurlwithsameportaswebservice/cxf/test/monitor");

socket.onmessage= function(e) { console.log(e.data); };

What's wrong?

Regards,
JP