anchor.diff:  If you need to configure your embdedded servlet container programmatically you can register
   a Spring bean that implements the `EmbeddedServletContainerCustomizer` interface.
   `EmbeddedServletContainerCustomizer` provides access to the
  -`ConfigurableEmbeddedServletContainerFactory` which includes numerous customization
  -setter methods.
  +`ConfigurableEmbeddedServletContainer` which includes numerous customization setter
  +methods.
   
   [source,java,indent=0]
   ----
  
positive.code: 
  
  [[boot-features-customizing-configurableembeddedservletcontainerfactory-directly]]
  ===== Customizing ConfigurableEmbeddedServletContainerFactory directly
  If the above customization techniques are too limited, you can register the
  `TomcatEmbeddedServletContainerFactory` or `JettyEmbeddedServletContainerFactory` bean
  yourself.
  
negative.code: 	private static class MyCustomizer implements EmbeddedServletContainerCustomizer {
  
  		@Override
  		public void customize(ConfigurableEmbeddedServletContainer container) {
              container.addErrorPages(new ErrorPage(HttpStatus.BAD_REQUEST, "/400"));
  		}
  
  	}
  