Allow custom RequestMappingHandlerMapping

Extract the creation of RequestMappingHandlerMapping into protected
method to allow easier use of custom subclasses.

Issue: SPR-12746

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/WebMvcConfigurationSupport.java

 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -223,7 +223,7 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 	 */
 	@Bean
 	public RequestMappingHandlerMapping requestMappingHandlerMapping() {
-		RequestMappingHandlerMapping handlerMapping = new RequestMappingHandlerMapping();
+		RequestMappingHandlerMapping handlerMapping = createRequestMappingHandlerMapping();
 		handlerMapping.setOrder(0);
 		handlerMapping.setInterceptors(getInterceptors());
 		handlerMapping.setContentNegotiationManager(mvcContentNegotiationManager());
@@ -248,6 +248,14 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		return handlerMapping;
 	}
 
+	/**
+	 * Protected method for plugging in a custom sub-class of
+	 * {@link RequestMappingHandlerMapping}.
+	 */
+	protected RequestMappingHandlerMapping createRequestMappingHandlerMapping() {
+		return new RequestMappingHandlerMapping();
+	}
+
 	/**
 	 * Provide access to the shared handler interceptors used to configure
 	 * {@link HandlerMapping} instances with. This method cannot be overridden,