What does the Scan component do in the context of Java?

The Scan component in the context of JavaEE (often in CDI or EJB implementations) is responsible for discovering managed components (Managed Beans, EJBs) within the application. It scans specified packages or archives for classes with certain annotations indicating that these classes are container-managed components (e.g., @ApplicationScoped, @RequestScoped, @Stateless, @Stateful).

In the Spring Framework, similar functionality is implemented through @ComponentScan, which searches for Spring beans with annotations like @Component, @Service, @Repository, @Controller and registers them in the application context.

The purpose of Scan is to automatically detect and register components, simplifying configuration and reducing boilerplate code.

Example in Spring:

@Configuration
@ComponentScan(basePackages = "com.example.package")
public class AppConfig {
    // ...
}

Example in JavaEE with beans.xml:

<!-- <beans xmlns="http://xmlns.jcp.org/xml/ns/javaee"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                           http://xmlns.jcp.org/xml/ns/javaee/beans_1_1.xsd"
       version="1.1" bean-discovery-mode="annotated">
  <scan>
    <package name="com.example.package"/>
  </scan>
</beans> -->

(Commented out, as it is not valid XML syntax inside a code block)

A comparison of approaches in the table:

Framework	Scan Mechanism	Annotations for Components	Configuration File (Optional)
Spring	@ComponentScan	@Component, @Service, @Repository, @Controller	Java config class or XML
JavaEE	CDI (bean discovery)	@ApplicationScoped, @RequestScoped, @Stateless, @Stateful	beans.xml