Extend DefaultDispatcherServletCondition to check for a registration

...bean with no explicit @Bean DispatcherServlet. We still have to check
by bean name (slightly unfortunate, but we need to avoid instantiating
too early) so there's now another magic
bean name for the registration bean ("dispatcherServletRegistration")
that the user has to replace if he wants the registration without
defining a servlet @Bean

Fixes gh-482

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

@@ -62,6 +62,11 @@ public class DispatcherServletAutoConfiguration {
 	 */
 	public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
 
+	/*
+	 * The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
+	 */
+	public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";
+
 	@Configuration
 	@Conditional(DefaultDispatcherServletCondition.class)
 	@ConditionalOnClass(ServletRegistration.class)
@@ -78,10 +83,11 @@ public class DispatcherServletAutoConfiguration {
 			return new DispatcherServlet();
 		}
 
-		@Bean
+		@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
 		public ServletRegistrationBean dispatcherServletRegistration() {
 			ServletRegistrationBean registration = new ServletRegistrationBean(
 					dispatcherServlet(), this.server.getServletPath());
+			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
 			if (this.multipartConfig != null) {
 				registration.setMultipartConfig(this.multipartConfig);
 			}
@@ -97,6 +103,17 @@ public class DispatcherServletAutoConfiguration {
 				AnnotatedTypeMetadata metadata) {
 
 			ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
+
+			ConditionOutcome outcome = checkServlets(beanFactory);
+
+			if (!outcome.isMatch()) {
+				return outcome;
+			}
+
+			return checkServletRegistrations(beanFactory);
+		}
+
+		private ConditionOutcome checkServlets(ConfigurableListableBeanFactory beanFactory) {
 			List<String> servlets = Arrays.asList(beanFactory.getBeanNamesForType(
 					DispatcherServlet.class, false, false));
 			boolean containsDispatcherBean = beanFactory
@@ -117,9 +134,46 @@ public class DispatcherServletAutoConfiguration {
 				return ConditionOutcome.noMatch("found non-DispatcherServlet named "
 						+ DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
 			}
+
 			return ConditionOutcome
 					.match("one or more DispatcherServlets found and none is named "
 							+ DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
+
+		}
+
+		/**
+		 */
+		protected ConditionOutcome checkServletRegistrations(
+				ConfigurableListableBeanFactory beanFactory) {
+
+			List<String> registrations = Arrays.asList(beanFactory.getBeanNamesForType(
+					ServletRegistrationBean.class, false, false));
+			boolean containsDispatcherRegistrationBean = beanFactory
+					.containsBean(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
+
+			if (registrations.isEmpty()) {
+				if (containsDispatcherRegistrationBean) {
+					return ConditionOutcome
+							.noMatch("found no ServletRegistrationBean but a non-ServletRegistrationBean named "
+									+ DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
+				}
+				return ConditionOutcome.match("no ServletRegistrationBean found");
+			}
+
+			if (registrations.contains(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)) {
+				return ConditionOutcome.noMatch("found ServletRegistrationBean named "
+						+ DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
+			}
+			if (containsDispatcherRegistrationBean) {
+				return ConditionOutcome
+						.noMatch("found non-ServletRegistrationBean named "
+								+ DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
+			}
+
+			return ConditionOutcome
+					.match("one or more ServletRegistrationBeans is found and none is named "
+							+ DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
+
 		}
 
 	}

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/DispatcherServletAutoConfigurationTests.java

@@ -54,6 +54,21 @@ public class DispatcherServletAutoConfigurationTests {
 		assertEquals("[/]", registration.getUrlMappings().toString());
 	}
 
+	@Test
+	public void registrationOverride() throws Exception {
+		this.context = new AnnotationConfigWebApplicationContext();
+		this.context.register(CustomDispatcherRegistration.class,
+				ServerPropertiesAutoConfiguration.class,
+				DispatcherServletAutoConfiguration.class);
+		this.context.setServletContext(new MockServletContext());
+		this.context.refresh();
+		ServletRegistrationBean registration = this.context
+				.getBean(ServletRegistrationBean.class);
+		assertEquals("[/foo]", registration.getUrlMappings().toString());
+		assertEquals("customDispatcher", registration.getServletName());
+		assertEquals(0, this.context.getBeanNamesForType(DispatcherServlet.class).length);
+	}
+
 	@Test
 	public void servletPath() throws Exception {
 		this.context = new AnnotationConfigWebApplicationContext();
@@ -95,4 +110,15 @@ public class DispatcherServletAutoConfigurationTests {
 
 	}
 
+	@Configuration
+	protected static class CustomDispatcherRegistration {
+		@Bean
+		public ServletRegistrationBean dispatcherServletRegistration() {
+			ServletRegistrationBean registration = new ServletRegistrationBean(
+					new DispatcherServlet(), "/foo");
+			registration.setName("customDispatcher");
+			return registration;
+		}
+	}
+
 }