Developing Java Applications with Spring and Spring Boot

Illustrating how going from async to sync can be easy, but the opposite is not

Invariably, the question comes along--Do I need a synchronous or asynchronous API?

It's important to understand that reactive programming is not very effective unless the entire stack is reactive. Otherwise, we're simply blocking at some point, which causes the backpressure to not achieve much. That's a long-winded way of saying there is little value in making the web layer reactive if the underlying services are not.

However, it is very likely that we may produce a chunk of code that must be tapped by a non-reactive layer, hence, we have to wrap our asynchronous, non-blocking code with the means to block.

Let's explore async-to-sync by creating a BlockingImageService ...