@Component is Spring Framework’s annotation to automatically create an instance of this class when the application starts and register it with the application context.

@ConfigurationProperties is a Spring Boot annotation that labels this Spring bean as a source of configuration properties. It indicates that the prefix of such properties will be my.app.

xxxxxxxxxx

@Component

@ConfigurationProperties(prefix = "my.app")

public class MyCustomProperties {

  // if you need a default value, assign it here or the 

     constructor

  private String header;

  private String footer;

  // getters and setters

}

https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/