Pro Spring MVC with Webflux

[Claude Moore]

Hi authors,

first of all, good luck for your book ! I wish to ask you a question about WebFlux and, more generally, about reactive approach in Java.
I'm just approaching to this programming style, and at the moment the most important problem I can see in adopting reactive approach is the lack of (wide) support for relational databases.
Also , we have a number of already well established  application @Services in our programs, most of which  perform somehow data access, in a transactional way.  
As far as I know, a number of annotations like @Transactional rely upon ThreadLocal variables, and ThreadLocal doesn't cope well with reactive approach.
Is there a way to avoid throwing away all good old style code and somehow get any of the benefits of the reactive approach ? A better multi-threading without callback hell approach would be enough, at least as a first step.

Thanks in advance !

[Marten Deinum]

Spring (Boot) has out-of-the-box support for R2DBC and Spring has reactive transaction support with @Transactional. So even with a reactive approach it is now possible to expose your database in a reactive way.

[Claude Moore]

Thanks for your reply Marten ! Does it apply also for JPA ? I think that the short answer is 'no', I heard about an Hibernate project aimed to introduce support to Reactive DBMS, but I don't know what's the state of the art of such project...

[Marten Deinum]

JPA, currently, relies on JDBC and thus is blocking. There is Hibernate Reactive however that isn't really tailored to be used outside of Quarkus I believe. It doesn't integrate the common know Reactive libraries (RxJava and Project Reactor) but only supports Mutiny and AFAIK doesn't play nice with other Reactive implementations. Although you could use the regular Async API as it seems. BUt there still isn't support in Spring for that (nor would I expect that shortly) so you would have to write parts of the integration yourself I suspect.