DelegatingWebMvcConfiguration properly delegates extendHandlerExceptionResolvers

Also fixes the declared visibility of configurePathMatch and configureAsyncSupport.

Issue: SPR-14599
(cherry picked from commit d2e3a1a)

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -22,6 +22,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.format.FormatterRegistry;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.util.CollectionUtils;
 import org.springframework.validation.MessageCodesResolver;
 import org.springframework.validation.Validator;
 import org.springframework.web.method.support.HandlerMethodArgumentResolver;
@@ -29,7 +30,7 @@ import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
 import org.springframework.web.servlet.HandlerExceptionResolver;
 
 /**
- * A sub-class of {@code WebMvcConfigurationSupport} that detects and delegates
+ * A subclass of {@code WebMvcConfigurationSupport} that detects and delegates
  * to all beans of type {@link WebMvcConfigurer} allowing them to customize the
  * configuration provided by {@code WebMvcConfigurationSupport}. This is the
  * class actually imported by {@link EnableWebMvc @EnableWebMvc}.
@@ -45,16 +46,15 @@ public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
 
 	@Autowired(required = false)
 	public void setConfigurers(List<WebMvcConfigurer> configurers) {
-		if (configurers == null || configurers.isEmpty()) {
-			return;
+		if (!CollectionUtils.isEmpty(configurers)) {
+			this.configurers.addWebMvcConfigurers(configurers);
 		}
-		this.configurers.addWebMvcConfigurers(configurers);
 	}
 
 
 	@Override
-	protected void addInterceptors(InterceptorRegistry registry) {
-		this.configurers.addInterceptors(registry);
+	protected void configurePathMatch(PathMatchConfigurer configurer) {
+		this.configurers.configurePathMatch(configurer);
 	}
 
 	@Override
@@ -63,23 +63,23 @@ public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
 	}
 
 	@Override
-	public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
+	protected void configureAsyncSupport(AsyncSupportConfigurer configurer) {
 		this.configurers.configureAsyncSupport(configurer);
 	}
 
 	@Override
-	public void configurePathMatch(PathMatchConfigurer configurer) {
-		this.configurers.configurePathMatch(configurer);
+	protected void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
+		this.configurers.configureDefaultServletHandling(configurer);
 	}
 
 	@Override
-	protected void addViewControllers(ViewControllerRegistry registry) {
-		this.configurers.addViewControllers(registry);
+	protected void addFormatters(FormatterRegistry registry) {
+		this.configurers.addFormatters(registry);
 	}
 
 	@Override
-	protected void configureViewResolvers(ViewResolverRegistry registry) {
-		this.configurers.configureViewResolvers(registry);
+	protected void addInterceptors(InterceptorRegistry registry) {
+		this.configurers.addInterceptors(registry);
 	}
 
 	@Override
@@ -88,8 +88,18 @@ public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
 	}
 
 	@Override
-	protected void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
-		this.configurers.configureDefaultServletHandling(configurer);
+	protected void addCorsMappings(CorsRegistry registry) {
+		this.configurers.addCorsMappings(registry);
+	}
+
+	@Override
+	protected void addViewControllers(ViewControllerRegistry registry) {
+		this.configurers.addViewControllers(registry);
+	}
+
+	@Override
+	protected void configureViewResolvers(ViewResolverRegistry registry) {
+		this.configurers.configureViewResolvers(registry);
 	}
 
 	@Override
@@ -113,8 +123,13 @@ public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
 	}
 
 	@Override
-	protected void addFormatters(FormatterRegistry registry) {
-		this.configurers.addFormatters(registry);
+	protected void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+		this.configurers.configureHandlerExceptionResolvers(exceptionResolvers);
+	}
+
+	@Override
+	protected void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+		this.configurers.extendHandlerExceptionResolvers(exceptionResolvers);
 	}
 
 	@Override
@@ -127,14 +142,4 @@ public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
 		return this.configurers.getMessageCodesResolver();
 	}
 
-	@Override
-	protected void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
-		this.configurers.configureHandlerExceptionResolvers(exceptionResolvers);
-	}
-
-	@Override
-	protected void addCorsMappings(CorsRegistry registry) {
-		this.configurers.addCorsMappings(registry);
-	}
-
 }

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

@@ -315,7 +315,7 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 	 * @see PathMatchConfigurer
 	 * @since 4.0.3
 	 */
-	public void configurePathMatch(PathMatchConfigurer configurer) {
+	protected void configurePathMatch(PathMatchConfigurer configurer) {
 	}
 
 	/**
@@ -531,6 +531,13 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		return initializer;
 	}
 
+	/**
+	 * Override this method to configure asynchronous request processing options.
+	 * @see AsyncSupportConfigurer
+	 */
+	protected void configureAsyncSupport(AsyncSupportConfigurer configurer) {
+	}
+
 	/**
 	 * Return a {@link FormattingConversionService} for use with annotated
 	 * controller methods and the {@code spring:eval} JSP tag.
@@ -543,6 +550,12 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		return conversionService;
 	}
 
+	/**
+	 * Override this method to add custom {@link Converter}s and {@link Formatter}s.
+	 */
+	protected void addFormatters(FormatterRegistry registry) {
+	}
+
 	/**
 	 * Return a global {@link Validator} instance for example for validating
 	 * {@code @ModelAttribute} and {@code @RequestBody} method arguments.
@@ -762,19 +775,6 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		}
 	}
 
-	/**
-	 * Override this method to add custom {@link Converter}s and {@link Formatter}s.
-	 */
-	protected void addFormatters(FormatterRegistry registry) {
-	}
-
-	/**
-	 * Override this method to configure asynchronous request processing options.
-	 * @see AsyncSupportConfigurer
-	 */
-	public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
-	}
-
 	/**
 	 * Return an instance of {@link CompositeUriComponentsContributor} for use with
 	 * {@link org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder}.

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

@@ -46,51 +46,6 @@ import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandl
  */
 public interface WebMvcConfigurer {
 
-	/**
-	 * Add {@link Converter}s and {@link Formatter}s in addition to the ones
-	 * registered by default.
-	 */
-	void addFormatters(FormatterRegistry registry);
-
-	/**
-	 * Configure the {@link HttpMessageConverter}s to use for reading or writing
-	 * to the body of the request or response. If no converters are added, a
-	 * default list of converters is registered.
-	 * <p><strong>Note</strong> that adding converters to the list, turns off
-	 * default converter registration. To simply add a converter without impacting
-	 * default registration, consider using the method
-	 * {@link #extendMessageConverters(java.util.List)} instead.
-	 * @param converters initially an empty list of converters
-	 */
-	void configureMessageConverters(List<HttpMessageConverter<?>> converters);
-
-	/**
-	 * A hook for extending or modifying the list of converters after it has been
-	 * configured. This may be useful for example to allow default converters to
-	 * be registered and then insert a custom converter through this method.
-	 * @param converters the list of configured converters to extend.
-	 * @since 4.1.3
-	 */
-	void extendMessageConverters(List<HttpMessageConverter<?>> converters);
-
-	/**
-	 * Provide a custom {@link Validator} instead of the one created by default.
-	 * The default implementation, assuming JSR-303 is on the classpath, is:
-	 * {@link org.springframework.validation.beanvalidation.OptionalValidatorFactoryBean}.
-	 * Leave the return value as {@code null} to keep the default.
-	 */
-	Validator getValidator();
-
-	/**
-	 * Configure content negotiation options.
-	 */
-	void configureContentNegotiation(ContentNegotiationConfigurer configurer);
-
-	/**
-	 * Configure asynchronous request handling options.
-	 */
-	void configureAsyncSupport(AsyncSupportConfigurer configurer);
-
 	/**
 	 * Helps with configuring HandlerMappings path matching options such as trailing slash match,
 	 * suffix registration, path matcher and path helper.
@@ -105,40 +60,28 @@ public interface WebMvcConfigurer {
 	void configurePathMatch(PathMatchConfigurer configurer);
 
 	/**
-	 * Add resolvers to support custom controller method argument types.
-	 * <p>This does not override the built-in support for resolving handler
-	 * method arguments. To customize the built-in support for argument
-	 * resolution, configure {@link RequestMappingHandlerAdapter} directly.
-	 * @param argumentResolvers initially an empty list
+	 * Configure content negotiation options.
 	 */
-	void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers);
+	void configureContentNegotiation(ContentNegotiationConfigurer configurer);
 
 	/**
-	 * Add handlers to support custom controller method return value types.
-	 * <p>Using this option does not override the built-in support for handling
-	 * return values. To customize the built-in support for handling return
-	 * values, configure RequestMappingHandlerAdapter directly.
-	 * @param returnValueHandlers initially an empty list
+	 * Configure asynchronous request handling options.
 	 */
-	void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers);
+	void configureAsyncSupport(AsyncSupportConfigurer configurer);
 
 	/**
-	 * Configure the {@link HandlerExceptionResolver}s to handle unresolved
-	 * controller exceptions. If no resolvers are added to the list, default
-	 * exception resolvers are added instead.
-	 * @param exceptionResolvers initially an empty list
+	 * Configure a handler to delegate unhandled requests by forwarding to the
+	 * Servlet container's "default" servlet. A common use case for this is when
+	 * the {@link DispatcherServlet} is mapped to "/" thus overriding the
+	 * Servlet container's default handling of static resources.
 	 */
-	void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers);
+	void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer);
 
 	/**
-	 * A hook for extending or modifying the list of
-	 * {@link HandlerExceptionResolver}s after it has been configured. This may
-	 * be useful for example to allow default resolvers to be registered and then
-	 * insert a custom one through this method.
-	 * @param exceptionResolvers the list of configured resolvers to extend.
-	 * @since 4.3
+	 * Add {@link Converter}s and {@link Formatter}s in addition to the ones
+	 * registered by default.
 	 */
-	void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers);
+	void addFormatters(FormatterRegistry registry);
 
 	/**
 	 * Add Spring MVC lifecycle interceptors for pre- and post-processing of
@@ -155,11 +98,17 @@ public interface WebMvcConfigurer {
 	void addInterceptors(InterceptorRegistry registry);
 
 	/**
-	 * Provide a custom {@link MessageCodesResolver} for building message codes
-	 * from data binding and validation error codes. Leave the return value as
-	 * {@code null} to keep the default.
+	 * Add handlers to serve static resources such as images, js, and, css
+	 * files from specific locations under web application root, the classpath,
+	 * and others.
 	 */
-	MessageCodesResolver getMessageCodesResolver();
+	void addResourceHandlers(ResourceHandlerRegistry registry);
+
+	/**
+	 * Configure cross origin requests processing.
+	 * @since 4.2
+	 */
+	void addCorsMappings(CorsRegistry registry);
 
 	/**
 	 * Configure simple automated controllers pre-configured with the response
@@ -178,24 +127,74 @@ public interface WebMvcConfigurer {
 	void configureViewResolvers(ViewResolverRegistry registry);
 
 	/**
-	 * Add handlers to serve static resources such as images, js, and, css
-	 * files from specific locations under web application root, the classpath,
-	 * and others.
+	 * Add resolvers to support custom controller method argument types.
+	 * <p>This does not override the built-in support for resolving handler
+	 * method arguments. To customize the built-in support for argument
+	 * resolution, configure {@link RequestMappingHandlerAdapter} directly.
+	 * @param argumentResolvers initially an empty list
 	 */
-	void addResourceHandlers(ResourceHandlerRegistry registry);
+	void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers);
 
 	/**
-	 * Configure a handler to delegate unhandled requests by forwarding to the
-	 * Servlet container's "default" servlet. A common use case for this is when
-	 * the {@link DispatcherServlet} is mapped to "/" thus overriding the
-	 * Servlet container's default handling of static resources.
+	 * Add handlers to support custom controller method return value types.
+	 * <p>Using this option does not override the built-in support for handling
+	 * return values. To customize the built-in support for handling return
+	 * values, configure RequestMappingHandlerAdapter directly.
+	 * @param returnValueHandlers initially an empty list
 	 */
-	void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer);
+	void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers);
 
 	/**
-	 * Configure cross origin requests processing.
-	 * @since 4.2
+	 * Configure the {@link HttpMessageConverter}s to use for reading or writing
+	 * to the body of the request or response. If no converters are added, a
+	 * default list of converters is registered.
+	 * <p><strong>Note</strong> that adding converters to the list, turns off
+	 * default converter registration. To simply add a converter without impacting
+	 * default registration, consider using the method
+	 * {@link #extendMessageConverters(java.util.List)} instead.
+	 * @param converters initially an empty list of converters
 	 */
-	void addCorsMappings(CorsRegistry registry);
+	void configureMessageConverters(List<HttpMessageConverter<?>> converters);
+
+	/**
+	 * A hook for extending or modifying the list of converters after it has been
+	 * configured. This may be useful for example to allow default converters to
+	 * be registered and then insert a custom converter through this method.
+	 * @param converters the list of configured converters to extend.
+	 * @since 4.1.3
+	 */
+	void extendMessageConverters(List<HttpMessageConverter<?>> converters);
+
+	/**
+	 * Configure the {@link HandlerExceptionResolver}s to handle unresolved
+	 * controller exceptions. If no resolvers are added to the list, default
+	 * exception resolvers are added instead.
+	 * @param exceptionResolvers initially an empty list
+	 */
+	void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers);
+
+	/**
+	 * A hook for extending or modifying the list of {@link HandlerExceptionResolver}s
+	 * after it has been configured. This may be useful for example to allow default
+	 * resolvers to be registered and then insert a custom one through this method.
+	 * @param exceptionResolvers the list of configured resolvers to extend
+	 * @since 4.3
+	 */
+	void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers);
+
+	/**
+	 * Provide a custom {@link Validator} instead of the one created by default.
+	 * The default implementation, assuming JSR-303 is on the classpath, is:
+	 * {@link org.springframework.validation.beanvalidation.OptionalValidatorFactoryBean}.
+	 * Leave the return value as {@code null} to keep the default.
+	 */
+	Validator getValidator();
+
+	/**
+	 * Provide a custom {@link MessageCodesResolver} for building message codes
+	 * from data binding and validation error codes. Leave the return value as
+	 * {@code null} to keep the default.
+	 */
+	MessageCodesResolver getMessageCodesResolver();
 
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -28,7 +28,7 @@ import org.springframework.web.servlet.HandlerExceptionResolver;
 
 /**
  * An implementation of {@link WebMvcConfigurer} with empty methods allowing
- * sub-classes to override only the methods they're interested in.
+ * subclasses to override only the methods they're interested in.
  *
  * @author Rossen Stoyanchev
  * @since 3.1
@@ -40,7 +40,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void addFormatters(FormatterRegistry registry) {
+	public void configurePathMatch(PathMatchConfigurer configurer) {
 	}
 
 	/**
@@ -48,7 +48,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
+	public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
 	}
 
 	/**
@@ -56,16 +56,15 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
+	public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
 	}
 
 	/**
 	 * {@inheritDoc}
-	 * <p>This implementation returns {@code null}
+	 * <p>This implementation is empty.
 	 */
 	@Override
-	public Validator getValidator() {
-		return null;
+	public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
 	}
 
 	/**
@@ -73,7 +72,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
+	public void addFormatters(FormatterRegistry registry) {
 	}
 
 	/**
@@ -81,7 +80,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
+	public void addInterceptors(InterceptorRegistry registry) {
 	}
 
 	/**
@@ -89,7 +88,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void configurePathMatch(PathMatchConfigurer configurer) {
+	public void addResourceHandlers(ResourceHandlerRegistry registry) {
 	}
 
 	/**
@@ -97,7 +96,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
+	public void addCorsMappings(CorsRegistry registry) {
 	}
 
 	/**
@@ -105,7 +104,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers) {
+	public void addViewControllers(ViewControllerRegistry registry) {
 	}
 
 	/**
@@ -113,7 +112,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+	public void configureViewResolvers(ViewResolverRegistry registry) {
 	}
 
 	/**
@@ -121,7 +120,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+	public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
 	}
 
 	/**
@@ -129,8 +128,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public MessageCodesResolver getMessageCodesResolver() {
-		return null;
+	public void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers) {
 	}
 
 	/**
@@ -138,7 +136,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void addInterceptors(InterceptorRegistry registry) {
+	public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
 	}
 
 	/**
@@ -146,7 +144,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void addViewControllers(ViewControllerRegistry registry) {
+	public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
 	}
 
 	/**
@@ -154,7 +152,7 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void configureViewResolvers(ViewResolverRegistry registry) {
+	public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
 	}
 
 	/**
@@ -162,23 +160,25 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	 * <p>This implementation is empty.
 	 */
 	@Override
-	public void addResourceHandlers(ResourceHandlerRegistry registry) {
+	public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
 	}
 
 	/**
 	 * {@inheritDoc}
-	 * <p>This implementation is empty.
+	 * <p>This implementation returns {@code null}.
 	 */
 	@Override
-	public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
+	public Validator getValidator() {
+		return null;
 	}
 
 	/**
 	 * {@inheritDoc}
-	 * <p>This implementation is empty.
+	 * <p>This implementation returns {@code null}.
 	 */
 	@Override
-	public void addCorsMappings(CorsRegistry registry) {
+	public MessageCodesResolver getMessageCodesResolver() {
+		return null;
 	}
 
 }

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

@@ -21,6 +21,7 @@ import java.util.List;
 
 import org.springframework.format.FormatterRegistry;
 import org.springframework.http.converter.HttpMessageConverter;
+import org.springframework.util.CollectionUtils;
 import org.springframework.validation.MessageCodesResolver;
 import org.springframework.validation.Validator;
 import org.springframework.web.method.support.HandlerMethodArgumentResolver;
@@ -37,16 +38,18 @@ class WebMvcConfigurerComposite implements WebMvcConfigurer {
 
 	private final List<WebMvcConfigurer> delegates = new ArrayList<WebMvcConfigurer>();
 
+
 	public void addWebMvcConfigurers(List<WebMvcConfigurer> configurers) {
-		if (configurers != null) {
+		if (!CollectionUtils.isEmpty(configurers)) {
 			this.delegates.addAll(configurers);
 		}
 	}
 
+
 	@Override
-	public void addFormatters(FormatterRegistry registry) {
+	public void configurePathMatch(PathMatchConfigurer configurer) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.addFormatters(registry);
+			delegate.configurePathMatch(configurer);
 		}
 	}
 
@@ -65,131 +68,126 @@ class WebMvcConfigurerComposite implements WebMvcConfigurer {
 	}
 
 	@Override
-	public void configurePathMatch(PathMatchConfigurer configurer) {
+	public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.configurePathMatch(configurer);
+			delegate.configureDefaultServletHandling(configurer);
 		}
 	}
 
 	@Override
-	public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
+	public void addFormatters(FormatterRegistry registry) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.configureMessageConverters(converters);
+			delegate.addFormatters(registry);
 		}
 	}
 
 	@Override
-	public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
+	public void addInterceptors(InterceptorRegistry registry) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.extendMessageConverters(converters);
+			delegate.addInterceptors(registry);
 		}
 	}
 
 	@Override
-	public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
+	public void addResourceHandlers(ResourceHandlerRegistry registry) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.addArgumentResolvers(argumentResolvers);
+			delegate.addResourceHandlers(registry);
 		}
 	}
 
 	@Override
-	public void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers) {
+	public void addCorsMappings(CorsRegistry registry) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.addReturnValueHandlers(returnValueHandlers);
+			delegate.addCorsMappings(registry);
 		}
 	}
 
 	@Override
-	public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+	public void addViewControllers(ViewControllerRegistry registry) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.configureHandlerExceptionResolvers(exceptionResolvers);
+			delegate.addViewControllers(registry);
 		}
 	}
 
 	@Override
-	public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+	public void configureViewResolvers(ViewResolverRegistry registry) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.configureHandlerExceptionResolvers(exceptionResolvers);
+			delegate.configureViewResolvers(registry);
 		}
 	}
 
 	@Override
-	public void addInterceptors(InterceptorRegistry registry) {
+	public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.addInterceptors(registry);
+			delegate.addArgumentResolvers(argumentResolvers);
 		}
 	}
 
 	@Override
-	public void addViewControllers(ViewControllerRegistry registry) {
+	public void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> returnValueHandlers) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.addViewControllers(registry);
+			delegate.addReturnValueHandlers(returnValueHandlers);
 		}
 	}
 
 	@Override
-	public void configureViewResolvers(ViewResolverRegistry registry) {
+	public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.configureViewResolvers(registry);
+			delegate.configureMessageConverters(converters);
 		}
 	}
 
 	@Override
-	public void addResourceHandlers(ResourceHandlerRegistry registry) {
+	public void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.addResourceHandlers(registry);
+			delegate.extendMessageConverters(converters);
 		}
 	}
 
 	@Override
-	public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
+	public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
 		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.configureDefaultServletHandling(configurer);
+			delegate.configureHandlerExceptionResolvers(exceptionResolvers);
+		}
+	}
+
+	@Override
+	public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+		for (WebMvcConfigurer delegate : this.delegates) {
+			delegate.extendHandlerExceptionResolvers(exceptionResolvers);
 		}
 	}
 
 	@Override
 	public Validator getValidator() {
-		List<Validator> candidates = new ArrayList<Validator>();
+		Validator selected = null;
 		for (WebMvcConfigurer configurer : this.delegates) {
 			Validator validator = configurer.getValidator();
 			if (validator != null) {
-				candidates.add(validator);
+				if (selected != null) {
+					throw new IllegalStateException("No unique Validator found: {" +
+							selected + ", " + validator + "}");
+				}
+				selected = validator;
 			}
 		}
-		return selectSingleInstance(candidates, Validator.class);
-	}
-
-	@Override
-	public void addCorsMappings(CorsRegistry registry) {
-		for (WebMvcConfigurer delegate : this.delegates) {
-			delegate.addCorsMappings(registry);
-		}
-	}
-
-	private <T> T selectSingleInstance(List<T> instances, Class<T> instanceType) {
-		if (instances.size() > 1) {
-			throw new IllegalStateException(
-					"Only one [" + instanceType + "] was expected but multiple instances were provided: " + instances);
-		}
-		else if (instances.size() == 1) {
-			return instances.get(0);
-		}
-		else {
-			return null;
-		}
+		return selected;
 	}
 
 	@Override
 	public MessageCodesResolver getMessageCodesResolver() {
-		List<MessageCodesResolver> candidates = new ArrayList<MessageCodesResolver>();
+		MessageCodesResolver selected = null;
 		for (WebMvcConfigurer configurer : this.delegates) {
 			MessageCodesResolver messageCodesResolver = configurer.getMessageCodesResolver();
 			if (messageCodesResolver != null) {
-				candidates.add(messageCodesResolver);
+				if (selected != null) {
+					throw new IllegalStateException("No unique MessageCodesResolver found: {" +
+							selected + ", " + messageCodesResolver + "}");
+				}
+				selected = messageCodesResolver;
 			}
 		}
-		return selectSingleInstance(candidates, MessageCodesResolver.class);
+		return selected;
 	}
 
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -17,7 +17,7 @@
 package org.springframework.web.servlet.config.annotation;
 
 import java.util.ArrayList;
-import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 
 import org.junit.Before;
@@ -89,10 +89,10 @@ public class DelegatingWebMvcConfigurationTests {
 		delegatingConfig = new DelegatingWebMvcConfiguration();
 	}
 
+
 	@Test
 	public void requestMappingHandlerAdapter() throws Exception {
-
-		delegatingConfig.setConfigurers(Arrays.asList(webMvcConfigurer));
+		delegatingConfig.setConfigurers(Collections.singletonList(webMvcConfigurer));
 		RequestMappingHandlerAdapter adapter = delegatingConfig.requestMappingHandlerAdapter();
 
 		ConfigurableWebBindingInitializer initializer = (ConfigurableWebBindingInitializer) adapter.getWebBindingInitializer();
@@ -141,7 +141,7 @@ public class DelegatingWebMvcConfigurationTests {
 	public void getCustomValidator() {
 		given(webMvcConfigurer.getValidator()).willReturn(new LocalValidatorFactoryBean());
 
-		delegatingConfig.setConfigurers(Arrays.asList(webMvcConfigurer));
+		delegatingConfig.setConfigurers(Collections.singletonList(webMvcConfigurer));
 		delegatingConfig.mvcValidator();
 
 		verify(webMvcConfigurer).getValidator();
@@ -151,7 +151,7 @@ public class DelegatingWebMvcConfigurationTests {
 	public void getCustomMessageCodesResolver() {
 		given(webMvcConfigurer.getMessageCodesResolver()).willReturn(new DefaultMessageCodesResolver());
 
-		delegatingConfig.setConfigurers(Arrays.asList(webMvcConfigurer));
+		delegatingConfig.setConfigurers(Collections.singletonList(webMvcConfigurer));
 		delegatingConfig.getMessageCodesResolver();
 
 		verify(webMvcConfigurer).getMessageCodesResolver();
@@ -159,8 +159,7 @@ public class DelegatingWebMvcConfigurationTests {
 
 	@Test
 	public void handlerExceptionResolver() throws Exception {
-
-		delegatingConfig.setConfigurers(Arrays.asList(webMvcConfigurer));
+		delegatingConfig.setConfigurers(Collections.singletonList(webMvcConfigurer));
 		delegatingConfig.handlerExceptionResolver();
 
 		verify(webMvcConfigurer).configureMessageConverters(converters.capture());
@@ -186,7 +185,7 @@ public class DelegatingWebMvcConfigurationTests {
 		delegatingConfig.setConfigurers(configurers);
 
 		HandlerExceptionResolverComposite composite =
-			(HandlerExceptionResolverComposite) delegatingConfig.handlerExceptionResolver();
+				(HandlerExceptionResolverComposite) delegatingConfig.handlerExceptionResolver();
 		assertEquals("Only one custom converter is expected", 1, composite.getExceptionResolvers().size());
 	}
 
@@ -200,9 +199,9 @@ public class DelegatingWebMvcConfigurationTests {
 			@Override
 			public void configurePathMatch(PathMatchConfigurer configurer) {
 				configurer.setUseRegisteredSuffixPatternMatch(true)
-					.setUseTrailingSlashMatch(false)
-					.setUrlPathHelper(pathHelper)
-					.setPathMatcher(pathMatcher);
+						.setUseTrailingSlashMatch(false)
+						.setUrlPathHelper(pathHelper)
+						.setPathMatcher(pathMatcher);
 			}
 		});
 		delegatingConfig.setConfigurers(configurers);