Spring Boot Internal Working

In a Spring Boot application, there is a single entry point that serves as the starting point for the application. This entry point is typically a Java class annotated with @SpringBootApplication, which combines several essential Spring annotations to enable auto-configuration, component scanning, and configuration as shown below:

Spring main class contains the main method, which calls SpringApplication.run(), bootstrapping the entire Spring Boot application.

@EnableAutoConfiguration

@EnableAutoConfiguration annotation helps us to configure things automatically. For Example, Spring automatically create connection and other required objects as soon as we add a data base dependency in pom.xml and declare configurations in application.properties.

@ComponentScan

@ComponentScan annotation tells spring application 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.

Follow link to read more about ComponentScan.

@Configuration

@Configuration annotation helps us to define a simple POJO class as bean with the help of @Bean annotation. Beans define with the help of @Configuration class are singleton classes.

@Configuration internally is a component as it implicitly uses @Component annotation similar of @Service and @Repository.