spring boot,Where's the Root WebApplicationContext and Servlet WebApplicationContext - spring

Question

I use spring-boot-starter-web 1.5.17.I can't find any auto configuration about build Root WebApplicationContext and Servlet WebApplicationContext.
When not use spring boot,we need do this
public class WebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
#Override
protected String[] getServletMappings() {
return new String[]{"/"};
}
#Override
protected Class<?>[] getRootConfigClasses() {
return new Class<?>[]{SecurityAdminConfig.class, DataSourceConfig.class, JavaConfig.class};
}
#Override
protected Class<?>[] getServletConfigClasses() {
return new Class<?>[]{WebMvcConfig.class};
}
//controller、service
I know WebMvcAutoConfiguration do a lot of spring MVC configuration,but i can't find about auto build Root WebApplicationContext and Servlet WebApplicationContext.
public abstract class AbstractAnnotationConfigDispatcherServletInitializer
extends AbstractDispatcherServletInitializer {
#Override
protected WebApplicationContext createRootApplicationContext() {
Class<?>[] configClasses = getRootConfigClasses();
if (!ObjectUtils.isEmpty(configClasses)) {
AnnotationConfigWebApplicationContext rootAppContext = new AnnotationConfigWebApplicationContext();
rootAppContext.register(configClasses);
return rootAppContext;
}
else {
return null;
}
}
#Override
protected WebApplicationContext createServletApplicationContext() {
AnnotationConfigWebApplicationContext servletAppContext = new AnnotationConfigWebApplicationContext();
Class<?>[] configClasses = getServletConfigClasses();
if (!ObjectUtils.isEmpty(configClasses)) {
servletAppContext.register(configClasses);
}
return servletAppContext;
}
protected abstract Class<?>[] getRootConfigClasses();
protected abstract Class<?>[] getServletConfigClasses();
}
How can know this beans go Root WebApplicationContext or Servlet WebApplicationContext?
image here

Answer 1

There is, by default, a single application context in a Spring Boot web (or otherwise) application. It is created by SpringApplication when your application starts.

Answer 2

The right way to do it would be this:
public class App {
public static void main(String[] args) {
new SpringApplicationBuilder()
.parent(ParentConfig.class).web(WebApplicationType.NONE)
.child(WebConfig.class).web(WebApplicationType.SERVLET)
.sibling(RestConfig.class).web(WebApplicationType.SERVLET)
.run(args);
}
}
I have taken it from here:
However, it is still not clear why by default everything is in the same context..
Also, I am not sure if that's fine that other beans created by WebMvcAutoconfiguration will be shared across all child contexts.