Which callback method is necessary only for invoking a SOAP service?

The correct answer is that the method necessary only for invoking a SOAP service is parseResponse. In the context of SOAP services, when a call is made, the server returns a response that is formatted in XML. The parseResponse method is critical for handling this XML response, as it involves interpreting the data and converting it into a usable format for the application.

This method ensures that the application can extract the relevant information from the complex XML structure that SOAP responses commonly have. It processes the output of the SOAP service and enables further action based on that data. Without this method, the application would be unable to properly utilize the information obtained from the SOAP service, making it a necessary component of the process.

While other methods like initServiceClient, createRequest, and mockCall may be important in various contexts, especially regarding setting up service clients or creating requests, they do not specifically apply only to SOAP services in the same way that parsing the XML response does.