Add option to extend exception resolvers

Issue: SPR-13931

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

@@ -713,6 +713,14 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 	protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
 	}
 
+	/**
+	 * Override this method to extend or modify 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
+	 */
 	protected void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
 	}
 
@@ -813,6 +821,7 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 			addDefaultHandlerExceptionResolvers(exceptionResolvers);
 		}
 
+		extendHandlerExceptionResolvers(exceptionResolvers);
 		HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();
 		composite.setOrder(0);
 		composite.setExceptionResolvers(exceptionResolvers);
@@ -831,6 +840,17 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 	protected void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
 	}
 
+	/**
+	 * Override this method to extend or modify 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 4.3.1
+	 */
+	protected void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+	}
+
 	/**
 	 * A method available to subclasses for adding default {@link HandlerExceptionResolver}s.
 	 * <p>Adds the following exception resolvers:

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/WebMvcConfigurer.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.
@@ -130,6 +130,16 @@ public interface WebMvcConfigurer {
 	 */
 	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 4.3.1
+	 */
+	void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers);
+
 	/**
 	 * Add Spring MVC lifecycle interceptors for pre- and post-processing of
 	 * controller method invocations. Interceptors can be registered to apply

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

@@ -116,6 +116,14 @@ public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {
 	public void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
 	}
 
+	/**
+	 * {@inheritDoc}
+	 * <p>This implementation is empty.
+	 */
+	@Override
+	public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+	}
+
 	/**
 	 * {@inheritDoc}
 	 * <p>This implementation is empty.

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/WebMvcConfigurerComposite.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.method.support.HandlerMethodReturnValueHandler;
 import org.springframework.web.servlet.HandlerExceptionResolver;
 
 /**
- * An {@link WebMvcConfigurer} implementation that delegates to other {@link WebMvcConfigurer} instances.
+ * A {@link WebMvcConfigurer} that delegates to one or more others.
  *
  * @author Rossen Stoyanchev
  * @since 3.1
@@ -106,6 +106,13 @@ class WebMvcConfigurerComposite implements WebMvcConfigurer {
 		}
 	}
 
+	@Override
+	public void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
+		for (WebMvcConfigurer delegate : this.delegates) {
+			delegate.configureHandlerExceptionResolvers(exceptionResolvers);
+		}
+	}
+
 	@Override
 	public void addInterceptors(InterceptorRegistry registry) {
 		for (WebMvcConfigurer delegate : this.delegates) {