Delving into Spring Boot's property support

We just got things off the ground with an operational application, but that isn't the only killer feature of Spring Boot.

Spring Boot comes with a fistful of prebuilt properties. In fact, just about every autoconfigured component has some property setting (http://docs.spring.io/spring-boot/docs/2.0.0.M5/reference/htmlsingle/#common-application-properties) allowing you to override just the parts you like.

Many of these autoconfigured beans will back off if Boot spots us creating our own. For example, when Spring Boot spots reactive MongoDB drivers on the classpath, it automatically creates a reactive MongoClient. However, if we define our own MongoClient bean, then Spring Boot will back off and accept ours.

This can lead to other components switching off. But sometimes, we don't need to swap out an entire bean. Instead, we may wish to merely tweak a single property of one of these autoconfigured beans.

Let's try to make some adjustments to src/main...