Which of these is a required step when integrating with the Web Service API via client code?

Integrating with the Web Service API via client code necessitates the generation of web service stubs as an essential step. Web service stubs are generated to facilitate communication between the client application and the Salesforce API. These stubs serve as a proxy, enabling the client code to interact with the remote web service without needing to worry about the underlying network protocols or message formats.

When you generate web service stubs, you create methods in your client code that correspond to the operations available in the Salesforce web service. These stubs ensure that your application can easily send requests to the Web Service API and handle responses effectively, streamlining the process of making API calls and improving overall development efficiency.

While the other options may pertain to various aspects of integration or Salesforce configurations, they are not mandatory steps specifically tied to the use of the Web Service API through client code. For instance, creating custom Salesforce objects is not required for basic API integration, generating API access keys pertains more to authentication rather than the integration process itself, and setting up external data sources relates to connecting third-party data sources rather than directly with the Web Service API. Thus, generating web service stubs is crucial as it forms the foundation for interacting with the API effectively.