How can versioning be implemented in Apex web services?

Implementing versioning in Apex web services is effectively achieved by creating classes with different URL mappings. This approach allows for the coexistence of multiple versions of the same web service, each identified by its unique URL. By specifying different URL mappings for each version, clients can access the desired service version without interference from updates or changes made to other versions.

This method is particularly beneficial in environments where backward compatibility needs to be maintained. For example, if an existing client relies on a particular version of the service, having distinct URL mappings ensures that they can continue to function without disruption, while new clients or updated versions can take advantage of the latest enhancements or changes.

When examining the other choices, creating multiple classes with the same URL mapping would lead to conflicts and ambiguity as to which class should handle the incoming request. Only creating a single version of the class prevents any flexibility and does not accommodate future changes or improvements. Lastly, simply changing parameters does not constitute a robust versioning strategy, as it can lead to confusion and errors, especially for clients relying on a known interface structure. Therefore, specifying different URL mappings is the most effective and organized way to implement versioning in Apex web services.