To invoke a Web Service upon sending a message to a channel, there are two options: SimpleWebServiceHandler and MarshallingWebServiceHandler. The former will accept either a String or javax.xml.transform.Source as the message payload. The latter provides support for any implementation of the Marshaller and Unmarshaller interfaces. Both require the URI of the Web Service to be called.

simpleHandler = new SimpleWebServiceHandler(uri);

marshallingHandler = new MarshallingWebServiceHandler(uri, marshaller);

Either adapter can then be referenced from a service-activator element that is subscribed to an input-channel. The endpoint is then responsible for passing the response to the proper reply channel. It will first check for an "output-channel" on the service-activator and will fallback to a RETURN_ADDRESS in the original message's headers.

For more detail on the inner workings, see the Spring Web Services reference guide's chapter covering client access as well as the chapter covering Object/XML mapping.