Add `createDispatcherServlet` hook point

Add an extra hook point in `AbstractDispatcherServletInitializer` to
customize the `DispatcherServlet`.

Issue: SPR-13222

spring-webmvc/src/main/java/org/springframework/web/servlet/support/AbstractDispatcherServletInitializer.java

@@ -53,6 +53,7 @@ import org.springframework.web.servlet.DispatcherServlet;
  * @author Chris Beams
  * @author Rossen Stoyanchev
  * @author Juergen Hoeller
+ * @author Stephane Nicoll
  * @since 3.2
  */
 public abstract class AbstractDispatcherServletInitializer extends AbstractContextLoaderInitializer {
@@ -76,7 +77,8 @@ public abstract class AbstractDispatcherServletInitializer extends AbstractConte
 	 * from {@link #createServletApplicationContext()}, and mapping it to the patterns
 	 * returned from {@link #getServletMappings()}.
 	 * <p>Further customization can be achieved by overriding {@link
-	 * #customizeRegistration(ServletRegistration.Dynamic)}.
+	 * #customizeRegistration(ServletRegistration.Dynamic)} or
+	 * {@link #createDispatcherServlet(WebApplicationContext)}.
 	 * @param servletContext the context to register the servlet against
 	 */
 	protected void registerDispatcherServlet(ServletContext servletContext) {
@@ -88,7 +90,7 @@ public abstract class AbstractDispatcherServletInitializer extends AbstractConte
 				"createServletApplicationContext() did not return an application " +
 				"context for servlet [" + servletName + "]");
 
-		DispatcherServlet dispatcherServlet = new DispatcherServlet(servletAppContext);
+		DispatcherServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
 		dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());
 
 		ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
@@ -129,6 +131,13 @@ public abstract class AbstractDispatcherServletInitializer extends AbstractConte
 	 */
 	protected abstract WebApplicationContext createServletApplicationContext();
 
+	/**
+	 * Create a {@link DispatcherServlet} with the specified {@link WebApplicationContext}.
+	 */
+	protected DispatcherServlet createDispatcherServlet(WebApplicationContext servletAppContext) {
+		return new DispatcherServlet(servletAppContext);
+	}
+
 	/**
 	 * Specify application context initializers to be applied to the servlet-specific
 	 * application context that the {@code DispatcherServlet} is being created with.

spring-webmvc/src/test/java/org/springframework/web/servlet/support/DispatcherServletInitializerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 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.
@@ -70,6 +70,7 @@ public class DispatcherServletInitializerTests {
 		assertNotNull(servlets.get(SERVLET_NAME));
 
 		DispatcherServlet servlet = (DispatcherServlet) servlets.get(SERVLET_NAME);
+		assertEquals(MyDispatcherServlet.class, servlet.getClass());
 		WebApplicationContext servletContext = servlet.getWebApplicationContext();
 
 		assertTrue(servletContext.containsBean("bean"));
@@ -84,6 +85,7 @@ public class DispatcherServletInitializerTests {
 		assertEquals(ROLE_NAME, registration.getRunAsRole());
 	}
 
+
 	private class MyMockServletContext extends MockServletContext {
 
 		@Override
@@ -104,6 +106,11 @@ public class DispatcherServletInitializerTests {
 			return SERVLET_NAME;
 		}
 
+		@Override
+		protected DispatcherServlet createDispatcherServlet(WebApplicationContext servletAppContext) {
+			return new MyDispatcherServlet(servletAppContext);
+		}
+
 		@Override
 		protected WebApplicationContext createServletApplicationContext() {
 			StaticWebApplicationContext servletContext =
@@ -129,7 +136,12 @@ public class DispatcherServletInitializerTests {
 	}
 
 	private static class MyBean {
+	}
 
+	private static class MyDispatcherServlet extends DispatcherServlet {
+		public MyDispatcherServlet(WebApplicationContext webApplicationContext) {
+			super(webApplicationContext);
+		}
 	}
 
 }

src/asciidoc/web-mvc.adoc

@@ -205,7 +205,7 @@ based equivalent of the above `web.xml` example:
 
 `WebApplicationInitializer` is an interface provided by Spring MVC that ensures your
 code-based configuration is detected and automatically used to initialize any Servlet 3
-container. An abstract base class implementation of this interace named
+container. An abstract base class implementation of this interface named
 `AbstractDispatcherServletInitializer` makes it even easier to register the
 `DispatcherServlet` by simply specifying its servlet mapping.
 See <<mvc-container-config,Code-based Servlet container initialization>> for more details.
@@ -4462,6 +4462,9 @@ The `isAsyncSupported` protected method of `AbstractDispatcherServletInitializer
 provides a single place to enable async support on the `DispatcherServlet` and all
 filters mapped to it. By default this flag is set to `true`.
 
+Finally, if you need to further customize the `DispatcherServlet` itself, you can
+override the `createDispatcherServlet` method.
+
 
 
 

src/asciidoc/whats-new.adoc

@@ -525,6 +525,8 @@ public @interface MyTestConfig {
 * When using GSON or Jackson 2.6+, the handler method return type is used to improve
   serialization of parameterized types like `List<Foo>`.
 * Default JSON prefix has been changed from "{} && " to the safer ")]}', " one.
+* Protected `createDispatcherServlet` method in `AbstractDispatcherServletInitializer` to further
+  customize the `DispatcherServlet` instance to use.
 
 === WebSocket Messaging Improvements