Hands-On Reactive Programming in Spring 5

Wrapping reactive transactions with the usingWhen factory

Similarly to the using operator, the usingWhen operator allows us manage resources in the reactive way. However, the using operator retrieves the managed resource synchronously (by calling the Callable instance). At the same time, the usingWhen operator retrieves the managed resource reactively (by subscribing to the instance of Publisher). Additionally, the usingWhen operator accepts different handlers for the successful and unsuccessful termination of the main processing stream. Those handlers are implemented by publishers. That distinction allows the implementation of completely non-blocking reactive transactions with only one operator. 

Let's assume we have an entirely reactive ...