"Say you send a SOAP message one-way over HTTP: the client's business logic triggers the SOAP layer to invoke the remote service. This causes an HTTP request to be sent to the server. When the request is received by the server, it should immediately return an HTTP response without servicing the request. The server-side business logic should run after the response has been returned. The response should not contain a SOAP message. An HTTP 200 or 202 status code response does not mean that the service completed successfully. A failure code, on the other hand, should guarantee that the service invocation failed. The SOAP layer on the client side blocks until it receives the response or times out."
You can also look at Mikalai Zaikin's guide regarding this.
Invokes a remote method using the one-way interaction mode. The client thread does not normally block waiting for the completion of the server processing for this remote method invocation. When the protocol in use is SOAP/HTTP, this method should block until an HTTP response code has been received or an error occurs. This method must not throw any remote exceptions. This method may throw a JAXRPCException during the processing of the one-way remote call.