JAX-WS endpoints delegate all marshalling/unmarshalling to the JAXB API. The most simple way to enable SwaRef encoding for DataHandler types is to annotate a payload bean with the @XmlAttachmentRef annotation as shown below:

/**
* Payload bean that will use SwaRef encoding
*/
@XmlRootElement
public class DocumentPayload
{
private DataHandler data;
  
public DocumentPayload()
{
}
  
public DocumentPayload(DataHandler data)
{
this.data = data;
}
  
@XmlElement
@XmlAttachmentRef
public DataHandler getData()
{
return data;
}
  
public void setData(DataHandler data)
{
this.data = data;
}
}

With document wrapped endpoints you may even specify the @XmlAttachmentRef annotation on the service endpoint interface:

@WebService
public interface DocWrappedEndpoint
{
@WebMethod
DocumentPayload beanAnnotation(DocumentPayload dhw, String test);
  
@WebMethod
@XmlAttachmentRef
DataHandler parameterAnnotation(@XmlAttachmentRef DataHandler data, String test);
  
}

The message would then refer to the attachment part by CID: