This is really a question for the Google Cloud Spanner Java API team...
Looking at the new Google Cloud Spanner service, it appears that the only way to perform read/write transactions is by providing a callback, via the TransactionRunner interface.
I understand that the API is trying to hide the details of the need to automatically retry transactions as a convenience to the programmer, but this limitation is a serious problem, at least for me. I need to be able to manage the transaction lifecycle myself, even if that means I have to perform my own retries (e.g., based on catching some sort of "retryable" exception).
To make this problem more concrete, suppose you wanted to implement Spring's PlatformTransactionManager for Google Cloud Spanner, so as to fit in with your existing code, and use your existing retry logic. It appears impossible to do that with the current Java API.
It seems like it would be easy to augment the API in a backward compatible way, to add a method returning a TransactionContext to the user, and let the user handle the retries.
Am I missing something? Can this alternate (more traditional) transaction API style be added to the Java API?
You are right in that TransactionRunner is the only way to do Read write transactions in the Java Client for Cloud Spanner. We believe that most users would prefer using that vs hand rolling their own retry logic. But we realize that it might not fit the needs of all the users and would love to hear about such use cases. Can you please file a feature request and we can further discuss there.