Seems that you are using Netty for HttpClient implementation.
Although async is not supported yet, maybe it would be better to use Reactor Netty instead for reactive support?

Adding reactive support would improve already existing implementation for Spring Oracle NoSQL SDK (currently it just wraps synchronous requests, that doesn't open real reactive programming perspectives) and allow using NoSQL SDK in real reactive environments.

If it is welcome, I can realize such functionality as separate module and send a pull request. But please, add at least a marker interface for oracle.nosql.driver.http.Client so driver (like QueryDriver) can set other client implementations.