Registering a Spring Bean using ApplicationContextInitializer

Spring Boot allows Builder to create customized Spring Boot application bootstrapping with a tool called SpringApplicationBuilder. This can be used as follows to customize the Spring Boot application and register a Spring Bean dynamically:

public static void main(String[] args) {
   new SpringApplicationBuilder(SpringBoot2IntroApplication.class)
         .bannerMode(Banner.Mode.OFF)
         .initializers((GenericApplicationContext 
           genericApplicationContext) -> {
            genericApplicationContext.registerBean
            ("internet",                               
             InternetHealthIndicator.class);
                       })

         .run(args);
}

In this code, a new instance of SpringApplicationBuilder is instantiated with a configuration class. By invoking the bannerMode(Banner.Mode.OFF) method, the banner shown in the console at the Spring Boot Bootstrap is switched off. 

By invoking the initializers() method with a lambda function (learn about lambda functions in the reference documentation at https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html) for ApplicationContextInitializer, the GenericApplicationContext.registerBean method is used to register a Spring Bean called internet and with class type InternetHealthIndicator.