docs: public void useAttachmentServiceWithWebClient() throws Exception {
  
          final String serviceURI = "http://localhost:" + port + "/services/attachments/multipart";
          
          
          JSONProvider provider = new JSONProvider();
          provider.setIgnoreNamespaces(true);
          provider.setInTransformElements(
              Collections.singletonMap("Book", "{http://books}Book"));
          
          WebClient client = WebClient.create(serviceURI,
                                       Collections.singletonList(provider));
          
          client.type("multipart/mixed").accept("multipart/mixed");
          
          MultipartBody body = createMultipartBody();
          
          System.out.println();
          System.out.println("Posting Book attachments with a WebClient");
          
          MultipartBody bodyResponse = client.post(body, MultipartBody.class);
          
          verifyMultipartResponse(bodyResponse);
      }