Writing java RestClient for webservice exposed as an interface(.class) and calling in async manner

I have to write a RestClient for a WebService which has been exposed as a Interface in a .class. The Interface is as

@Path("/read")
public interface IWebService {

    @POST
    @Path("/humanRollups")
    @Produces({"application/json"})
    @Consumes({"application/json"})
    public CustomResponse<List<HumanWrapper>> getHumansByIntelligence(          
            Request request, 
            @QueryParam("rgs") String rgsSet,
            @Context HttpHeaders httpHeaders);


}

I have to create a proxy out of this Interface and then the actual call to the Service should be make in an asynchronous manner (not using Executor thread pools). What is the best way to achieve the same?