Spring Boot by default will scan all the classes in the package the @SpringBootApplication class is defined in and all of its sub-packages. It will setup Spring Data JPA, scan for entities and what more in those packages.

Consider the following configuration 

@SpringBootApplication(scanBasePackages={"package1", "package2"})
public class MyApplication { ... }

Currently this configuration extends the packages scanned by the @ComponentScan defined on @SpringBootApplication. However if one also has entities or Spring Data repositories in those packages one needs to add additional annotations for configuration. 

@SpringBootApplication(scanBasePackages={"package1", "package2"})
@EntityScan(basePackages = {"package1", "package2"})
@EnableJpaRepositories(basePackages = {"package1", "package2"}))
public class MyApplication { ... }

Depending on what is used in the application there might be more configuration needed and it might also lead to disabling some auto-configuration I suspect (due to beans being loaded by the @Enable* annotations).

It would be a nice extension if the scanBasePackages could be extended to all other scanning parts as well. There is the @AutoConfigurationPackage annotation which provides this support for starters/auto-configuration. Couldn't the @SpringBootApplication annotation benefit from this as well and be an improvement on the user experience?

Comment From: snicoll

There is the @AutoConfigurationPackage annotation which provides this support for starters/auto-configuration.

What makes you think this is specific to starters or auto-configuration?

See also https://github.com/spring-projects/spring-boot/issues/27549

Comment From: mdeinum

Actually, I don't know, that was an (apparently) false assumption. Now there was a thing about assumptions.

Now I'm also calling my sanity as apparently I already registered the same issue and I didn't look (sorry for that, Monday and I need more coffee).

Nonetheless, I think that scanning multiple packages might have a bit more love. Currently, it needs putting more annotations on to configure it, but I also realize that there might be consequences that I don't oversee.

I did a small test locally and at first sight, it appears to be running fine when I add @AutoConfigurePackage to the @SpringBootApplication annotation and change the aliases from @ComponentScan to @AutoConfigurePackage. At least ./gradlew check runs without problems.

Comment From: snicoll

Let's close this one in favor of the documentation.