title: Cannot extend WebMvcAutoConfigurationAdapter in Spring Boot 1.4
body: <p>I'd like to update a web project to Spring Boot 1.4 but I'm getting and error.</p>
  
  <p>I'm currently using Spring Boot 1.3.3 and I'm extending <code>WebMvcAutoConfigurationAdapter</code> to map some custom resource hanlders:</p>
  
  <pre><code>@Configuration
  public class MvcConfiguration extends WebMvcAutoConfigurationAdapter {
  
      @Override
      public void addResourceHandlers(ResourceHandlerRegistry registry) {
          super.addResourceHandlers(registry);
          registry.addResourceHandler("/images/users/**").addResourceLocations("http://file-storage/images/users/");
          // ...
  
  }
  </code></pre>
  
  <p>I noticed that in the new version of SB a constructor was added to <code>WebMvcAutoConfigurationAdapter</code>:</p>
  
  <pre><code>public WebMvcAutoConfigurationAdapter(ResourceProperties resourceProperties,
          WebMvcProperties mvcProperties, ListableBeanFactory beanFactory,
          HttpMessageConverters messageConverters,
          ObjectProvider&lt;ResourceHandlerRegistrationCustomizer&gt; resourceHandlerRegistrationCustomizerProvider) {} 
  </code></pre>
  
  <p>and this constructor uses <code>ResourceHandlerRegistrationCustomizer</code> that is a package-protected interface, so, basically, from version 1.4 is not possible to extend autoconfiguration.</p>
  
  <p>What is an alternative way to extend autoconfiguration?</p>