What is component scanning in Spring?

Component scanning is the process where Spring walks a specified package (and its sub-packages) at startup, looking for classes annotated with @Component or one of its stereotypes, and automatically registers each one as a bean - no manual @Bean method needed for every class.

@SpringBootApplication
// implies @ComponentScan on the current package
public class ShopApplication {
    public static void main(String[] args) {
        SpringApplication.run(ShopApplication.class, args);
    }
}

It's triggered by @ComponentScan, which @SpringBootApplication already includes by default, scoped to the package the main class lives in and everything beneath it. Classes outside that package tree are simply invisible to the scan unless the base package is widened explicitly.

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