Add default ViewResolver to MVC Java config

Since the MVC Java config always registers a ViewResolver (composite)
bean, at a very minimum we must add an InternalResourceViewResolver
consistent with default DispatcherServlet configuration and by
extension with the MVC namespace which falls back on DispatcherServlet
implicity if no <view-resolvers> element is present.

Issue: SPR-7093

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

@@ -81,6 +81,7 @@ import org.springframework.web.servlet.mvc.method.annotation.ResponseBodyAdvice;
 import org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver;
 import org.springframework.web.servlet.resource.ResourceUrlProvider;
 import org.springframework.web.servlet.resource.ResourceUrlProviderExposingInterceptor;
+import org.springframework.web.servlet.view.InternalResourceViewResolver;
 import org.springframework.web.servlet.view.ViewResolverComposite;
 import org.springframework.web.util.UrlPathHelper;
 
@@ -779,6 +780,9 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 	 * {@link org.springframework.core.Ordered#HIGHEST_PRECEDENCE
 	 * Ordered.HIGHEST_PRECEDENCE}.
 	 *
+	 * <p>An {@code InternalResourceViewResolver} is added by default if no other
+	 * resolvers are configured.
+	 *
 	 * @since 4.1
 	 */
 	@Bean
@@ -788,9 +792,14 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		registry.setApplicationContext(this.applicationContext);
 		configureViewResolvers(registry);
 
+		List<ViewResolver> viewResolvers = registry.getViewResolvers();
+		if (viewResolvers.isEmpty()) {
+			viewResolvers.add(new InternalResourceViewResolver());
+		}
+
 		ViewResolverComposite composite = new ViewResolverComposite();
 		composite.setOrder(registry.getOrder());
-		composite.setViewResolvers(registry.getViewResolvers());
+		composite.setViewResolvers(viewResolvers);
 		composite.setApplicationContext(this.applicationContext);
 		composite.setServletContext(this.servletContext);
 		return composite;

spring-webmvc/src/test/java/org/springframework/web/servlet/config/annotation/WebMvcConfigurationSupportTests.java

@@ -49,6 +49,7 @@ import org.springframework.web.method.support.CompositeUriComponentsContributor;
 import org.springframework.web.servlet.HandlerExceptionResolver;
 import org.springframework.web.servlet.HandlerExecutionChain;
 import org.springframework.web.servlet.ViewResolver;
+import org.springframework.web.servlet.view.InternalResourceViewResolver;
 import org.springframework.web.servlet.view.ViewResolverComposite;
 import org.springframework.web.servlet.handler.AbstractHandlerMapping;
 import org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping;
@@ -208,7 +209,8 @@ public class WebMvcConfigurationSupportTests {
 		ViewResolverComposite compositeResolver = this.wac.getBean(ViewResolverComposite.class);
 		assertEquals(Ordered.LOWEST_PRECEDENCE, compositeResolver.getOrder());
 		List<ViewResolver> resolvers = compositeResolver.getViewResolvers();
-		assertEquals(0, resolvers.size());
+		assertEquals(1, resolvers.size());
+		assertEquals(InternalResourceViewResolver.class, resolvers.get(0).getClass());
 	}
 
 	@Test