org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [com.package.Response] and content type [application/octet-stream] @RestService RestClient restClient; ... String json = "{"param":3}"; restClient.getRestTemplate().getMessageConverters().add(new GsonHttpMessageConverter()); Response res = restClient.send(json); @Rest("http://my-url.com") public interface RestClient { @Post("/something/") Response send(String json); RestTemplate getRestTemplate(); void setRestTemplate(RestTemplate restTemplate); }