ExecutionContext executionContext = createExecutionContext();
executionContext.setSigner(signer);
executionContext.setCredentials(credentials);
StaxResponseHandler<X> responseHandler = new com.amazonaws.services.simpledb.internal.SimpleDBStaxResponseHandler<X>(unmarshaller);
DefaultErrorResponseHandler errorResponseHandler = new DefaultErrorResponseHandler(exceptionUnmarshallers);
return (X)client.execute(request, responseHandler, errorResponseHandler, executionContext);
}