anchor.diff:  [source,java,indent=0,subs="verbatim,quotes,attributes"]
   ----
   	import org.springframework.boot.autoconfigure.SpringBootApplication;
  -	import org.springframework.boot.context.web.SpringBootServletInitializer;
  +	import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;
   	import org.springframework.web.WebApplicationInitializer;
   
   	@SpringBootApplication
  
positive.code: [[howto-discover-the-http-port-at-runtime]]
  === Discover the HTTP Port at Runtime
  You can access the port the server is running on from log output or from the
  `ServletWebServerApplicationContext` through its `EmbeddedWebServer`. The best way to get
  that and be sure that it has been initialized is to add a `@Bean` of type
  `ApplicationListener<ServletWebServerInitializedEvent>` and pull the container
  out of the event when it is published.
  
  
negative.code: Generally you can follow the advice from
  "`<<howto-discover-build-in-options-for-external-properties>>`" about
  `@ConfigurationProperties` (`ServerProperties` and `ServerProperties.Undertow` are the
  main ones here). However, you should also look at `WebServerFactoryCustomizer`.
  Once you have access to the `UndertowServletWebServerFactory`, you can use an
  `UndertowBuilderCustomizer` to modify Undertow's configuration to meet your needs.
  Alternatively, if you need more control and customization, you can add your own
  