I tried to upload an attachment via Multipart. For that i use the client proxy api.
The proxy interface has a method like this:
When i generate the proxy with the old ProxyFactory it can send the POST, but an exception is thrown with the new ResteasyClientBuilder:
The problem seems to be, that the variable "annotations" in ResteasyProviderFactory.getClientMessageBodyWriter() is not correctly filled with a proxy generated by the new ResteasyClientBuilder. Without it, the correct MessageBodyWriter(MultipartFormAnnotationWriter) is not used.
The test project i used is attached.