@ComponentScan Annotation

The @ComponentScan annotation scans and registers all classes annotated with @Configuration, @Controller, @Service, @Repository, and other Spring-managed components.

@ComponentScan tells spring for where to search for all the classes annotated as @Configurations, @Controllers, @Service, @Repository, etc. annotations with the help of basePackageClasses() and basePackages().

Spring by default consider the package having @ComponentScan Annotation and all of its child packages to look for classes having @Configurations, @Controllers, @Service, @Repository, etc.

By default, @SpringBootApplication annotation contains @ComponentScan which consider current and all of its child packages to scan.

Below is an example, where we have declared @ComponentScan annotation having basePackages as attribute and value as com.example.demo. This means, spring will only consider com.example.demo and all of its child packages. It will NOT consider other parallel/sibling packages. such as com.example.practice.

Conclusion:

• @ComponentScan annotation directs Spring to scan and register classes annotated with @Configuration, @Controller, @Service, @Repository, and other Spring components.
• By default, it scans the package where it is declared and all its subpackages.
• The @SpringBootApplication annotation implicitly includes @ComponentScan, applying the same behavior. However, specifying the basePackages attribute in @ComponentScan restricts the scanning to specific packages and their subpackages while excluding sibling packages.