Use of #Import Annotation - spring-security

Question

I have started working on Spring Security. I am doing a HelloWorld application from this link.
My question is, why do we need the #Import annotation?
While working on Spring MVC, I used to define a similar configuration file, but since it was in the same package, I did not need to import it. Why am I importing the SecurityConfig.java file here, then?
The place where I have used the #Import annotation is here
AppConfig.java:
package com.mkyong.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.view.InternalResourceViewResolver;
import org.springframework.web.servlet.view.JstlView;
#EnableWebMvc
#Configuration
#ComponentScan({ "com.mkyong.web.*" })
#Import({ SecurityConfig.class })
public class AppConfig {
#Bean
public InternalResourceViewResolver viewResolver() {
InternalResourceViewResolver viewResolver
= new InternalResourceViewResolver();
viewResolver.setViewClass(JstlView.class);
viewResolver.setPrefix("/WEB-INF/pages/");
viewResolver.setSuffix(".jsp");
return viewResolver;
}
}

Answer 1

You need to import the security into the main app config class because it won't be picked up by the #ComponentScan because the class is not within the package for scanning #ComponentScan({ "com.mkyong.web.*" }). The security config is not defined in there. You register your main class like:
#Override
protected Class<?>[] getRootConfigClasses() {
return new Class[] { AppConfig.class };
}
If you don't import the security class into it then the security won't be registered in the application.