Switch RequestContextListener to Filter

Update WebMvcAutoConfiguration to use a RequestContextFilter instead of
a RequestContextListener.

Using a filter is required for some Spring Session operations (see
https://github.com/spring-projects/spring-session/issues/129).

This update also has the added benefit of allowing the Response to be
accessed from RequestContextHolder.getRequestAttributes() by casting it
to ServletRequestAttributes.

Fixes gh-2637

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/WebMvcAutoConfiguration.java

@@ -42,6 +42,7 @@ import org.springframework.boot.autoconfigure.web.ResourceProperties.Strategy;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.context.web.OrderedHiddenHttpMethodFilter;
 import org.springframework.boot.context.web.OrderedHttpPutFormContentFilter;
+import org.springframework.boot.context.web.OrderedRequestContextFilter;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
@@ -61,6 +62,7 @@ import org.springframework.web.bind.support.ConfigurableWebBindingInitializer;
 import org.springframework.web.context.request.RequestContextListener;
 import org.springframework.web.filter.HiddenHttpMethodFilter;
 import org.springframework.web.filter.HttpPutFormContentFilter;
+import org.springframework.web.filter.RequestContextFilter;
 import org.springframework.web.servlet.DispatcherServlet;
 import org.springframework.web.servlet.LocaleResolver;
 import org.springframework.web.servlet.View;
@@ -163,9 +165,10 @@ public class WebMvcAutoConfiguration {
 		}
 
 		@Bean
-		@ConditionalOnMissingBean
-		public RequestContextListener requestContextListener() {
-			return new RequestContextListener();
+		@ConditionalOnMissingBean({ RequestContextListener.class,
+				RequestContextFilter.class })
+		public RequestContextFilter requestContextFilter() {
+			return new OrderedRequestContextFilter();
 		}
 
 		@Bean