Allow default DispatcherServlet to be switched off more easily

All a user has to do now is declare a bean with name "dispatcherServlet".

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

@@ -17,6 +17,7 @@
 package org.springframework.boot.autoconfigure.web;
 
 import java.util.Arrays;
+import java.util.List;
 
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
@@ -72,15 +73,26 @@ public class DispatcherServletAutoConfiguration {
 				AnnotatedTypeMetadata metadata) {
 
 			ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
-			String[] beans = beanFactory.getBeanNamesForType(DispatcherServlet.class,
+			List<String> servlets = Arrays.asList(beanFactory.getBeanNamesForType(
-					false, false);
+					DispatcherServlet.class, false, false));
-			if (beans.length == 0) {
+			boolean containsDispatcherBean = beanFactory
+					.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
+			if (servlets.isEmpty()) {
+				if (containsDispatcherBean) {
+					return ConditionOutcome
+							.noMatch("found no DispatcherServlet but a non-DispatcherServlet named "
+									+ DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
+				}
 				return ConditionOutcome.match("no DispatcherServlet found");
 			}
-			if (Arrays.asList(beans).contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
+			if (servlets.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
 				return ConditionOutcome.noMatch("found DispatcherServlet named "
 						+ DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
 			}
+			if (containsDispatcherBean) {
+				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);

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

@@ -17,6 +17,8 @@
 package org.springframework.boot.autoconfigure.web;
 
 import javax.servlet.Servlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
 
 import org.junit.Test;
 import org.springframework.beans.BeansException;
@@ -32,6 +34,7 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.stereotype.Component;
 import org.springframework.web.servlet.DispatcherServlet;
+import org.springframework.web.servlet.FrameworkServlet;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNull;
@@ -75,6 +78,27 @@ public class EmbeddedServletContainerAutoConfigurationTests {
 		assertEquals(2, this.context.getBeanNamesForType(DispatcherServlet.class).length);
 	}
 
+	@Test
+	public void contextAlreadyHasNonDispatcherServlet() throws Exception {
+		this.context = new AnnotationConfigEmbeddedWebApplicationContext(
+				NonSpringServletConfiguration.class,
+				EmbeddedContainerConfiguration.class,
+				EmbeddedServletContainerAutoConfiguration.class,
+				DispatcherServletAutoConfiguration.class);
+		verifyContext(); // the non default servlet is still registered
+		assertEquals(0, this.context.getBeanNamesForType(DispatcherServlet.class).length);
+	}
+
+	@Test
+	public void contextAlreadyHasNonServlet() throws Exception {
+		this.context = new AnnotationConfigEmbeddedWebApplicationContext(
+				NonServletConfiguration.class, EmbeddedContainerConfiguration.class,
+				EmbeddedServletContainerAutoConfiguration.class,
+				DispatcherServletAutoConfiguration.class);
+		assertEquals(0, this.context.getBeanNamesForType(DispatcherServlet.class).length);
+		assertEquals(0, this.context.getBeanNamesForType(Servlet.class).length);
+	}
+
 	@Test
 	public void contextAlreadyHasDispatcherServletAndRegistration() throws Exception {
 		this.context = new AnnotationConfigEmbeddedWebApplicationContext(
@@ -151,6 +175,31 @@ public class EmbeddedServletContainerAutoConfigurationTests {
 
 	}
 
+	@Configuration
+	public static class NonSpringServletConfiguration {
+
+		@Bean
+		public Servlet dispatcherServlet() {
+			return new FrameworkServlet() {
+				@Override
+				protected void doService(HttpServletRequest request,
+						HttpServletResponse response) throws Exception {
+				}
+			};
+		}
+
+	}
+
+	@Configuration
+	public static class NonServletConfiguration {
+
+		@Bean
+		public String dispatcherServlet() {
+			return "foo";
+		}
+
+	}
+
 	@Configuration
 	public static class DispatcherServletWithRegistrationConfiguration {