Spring asyncRestTemplate for SOAP Services - spring

Question

I am trying to call a soap service using Spring's AsyncRestTemplate.
I know that AsyncRestTemplate supports only rest call and spring-ws is there if we need to make soap calls. But Spring-ws doesn't support Async calls and uses JDK's HttpURLConnection class for doing http call and I wanted to make async soap webservices call.
Below is my code for creating the soapenvelop using JDKs saaj api.
public SOAPEnvelope createSoapEnvelope(Employee obj){
MessageFactory factory = MessageFactory.newInstance();
SOAPMessage message = factory.createMessage();
SOAPPart soapPart = message.getSOAPPart();
try {
SOAPEnvelope envelope = soapPart.getEnvelope();
SOAPBody body = envelope.getBody();
QName bodyName = new QName(Constants.SERVICE_NAMESPACE);
SOAPBodyElement bodyElement = body.addBodyElement(bodyName);
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
Document document = db.newDocument();
// Marshal the Object to a Document
Marshaller marshaller = jaxbContext.createMarshaller();
marshaller.marshal(obj, document);
body.addDocument(document);
return envelope;
}catch (SOAPException | JAXBException | ParserConfigurationException e){
LOGGER.error("Unable to marshal ",e);
}
return null;
}
I set this soap envelop in HttpEntity to make the call though rest template like below
MultiValueMap headers = new HttpHeaders();
headers.set(HttpHeaders.ACCEPT,"text/xml;charset=UTF-8");
headers.set(HttpHeaders.CONTENT_TYPE,"text/xml;charset=UTF-8");
headers.set(HttpHeaders.ACCEPT_ENCODING,"gzip,deflate");
headers.set("SOAPAction", Constants.SOAP_ACTION);
HttpEntity<SOAPEnvelope> soapEntity = new HttpEntity<>(soapEnvelope,headers);
ListenableFuture<ResponseEntity<SOAPEnvelope>> future=
restTemplate.postForEntity(url,
,soapEntity,SOAPEnvelope.class);
After doing this I get exception org.springframework.web.client.RestClientException: Could not write request: no suitable HttpMessageConverter found for request type [com.sun.xml.internal.messaging.saaj.soap.ver1_1.Envelope1_1Impl] and content type [text/xml;charset=UTF-8]
I understood from this exception that Spring's HttpMessageConverters are not able to marshal SoapEnvelop and that's why this client is not able to submit the request.
I need help in writing custom message converter and registering it with rest template. All suggestions are welcome.
Thanks