Appendix C. Configuration properties
Although Spring Boot handles a lot of the grunt work when it comes to configuring the components in your application, you may want to fine-tune some of those components. That’s where configuration properties come in handy.
Chapter 3 describes the @ConfigurationProperties annotation and how it can be used to expose properties that you can configure external to application code. Just as you can use @ConfigurationProperties in components that you create, many of Spring Boot’s auto-configured components are also annotated with @ConfigurationProperties, making it possible to configure them via any supported property source.
For example, to specify the port that an embedded Tomcat or Jetty server should listen ...