The Spring Boot documentation for @SpringBootApplication states
Many Spring Boot developers always have their main class annotated
with@Configuration,@EnableAutoConfigurationand@ComponentScan.
Since these annotations are so frequently used together (especially if
you follow the best practices above), Spring Boot provides a
convenient@SpringBootApplicationalternative.The
@SpringBootApplicationannotation is equivalent to using
@Configuration,@EnableAutoConfigurationand@ComponentScanwith their
default attributes: […]
where the @ComponentScan javadoc states
If specific packages are not defined, scanning will occur from the
package of the class that declares this annotation.
That is, only the types that are in the same package as your ReadingListApplication will be scanned.
If you want a custom configuration, provide your own @Configuration, @EnableAutoConfiguration, and @ComponentScan, as appropriate.