notes/pl/java/libfws/spring/features/cfg/auto-config.txt

https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-developing-auto-configuration.html

so steps are
1. create a file in resources/META-INF/spring.factories
2. Create a class e.g. MapperAutoConfiguration
3. In spring.factories file add a line

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.clarabride.whateverpackagehere.MapperAutoConfiguration

in new created configuration class
define a bean
and put annotation on it
@OnMissingBean(SPMapper.class)

To summarize
1. Autoconfiguration applies at the end when all bean difinitions are read
2. @OnMissingBean(SPMapper.class) annotation prevents bean creation if it was already registered example

@Configuration
public class MapperAutoConfiguration {
    @Bean
    @ConditionalOnMissingBean
    public SPMapper myService() { ... } //return default mapper here
}

2019
https://spring.io/blog/2019/01/21/manual-bean-definitions-in-spring-boot