Spring Boot ApplicationContext

The primary job of the ApplicationContext is to manage beans.
let’s create a configuration class to define our AccountService class as a Spring bean:

@Configuration
public class AccountConfig {

  @Bean
  public AccountService accountService() {
    return new AccountService(accountRepository());
  }

  @Bean
  public AccountRepository accountRepository() {
    return new AccountRepository();
  }
}

Java configuration typically uses @Bean-annotated methods within a @Configuration class. The @Bean annotation on a method indicates that the method creates a Spring bean. Moreover, a class annotated with @Configuration indicates that it contains Spring bean configurations.

AnnotationConfigApplicationContext

ApplicationContext context = new AnnotationConfigApplicationContext(AccountConfig.class);
AccountService accountService = context.getBean(AccountService.class);

AnnotationConfigWebApplicationContext

is a web-based variant of AnnotationConfigApplicationContext.

We may use this class when we configure Spring’s ContextLoaderListener servlet listener or a Spring MVC DispatcherServlet in a web.xml file.

Moreover, from Spring 3.0 onward, we can also configure this application context container programmatically. All we need to do is implement the WebApplicationInitializer interface:

public class MyWebApplicationInitializer implements WebApplicationInitializer {

  public void onStartup(ServletContext container) throws ServletException {
    AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
    context.register(AccountConfig.class);
    context.setServletContext(container);

    // servlet configuration
  }
}

@Autowire  ApplicationContext

You can Autowire the ApplicationContext, either as a field

@Autowired
private ApplicationContext context;

or a method

@Autowired
public void context(ApplicationContext context) { this.context = context; }

Finally use

context.getBean(SomeClass.class)

References
https://www.baeldung.com/spring-application-context
https://stackoverflow.com/questions/34088780/how-to-get-bean-using-application-context-in-spring-boot