diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java
index 849abfc91c..887c0e2125 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfigurationTests.java
@@ -16,16 +16,17 @@
 
 package org.springframework.boot.autoconfigure.web.reactive;
 
+import org.apache.catalina.startup.Tomcat;
+import org.eclipse.jetty.server.Server;
 import org.junit.Test;
 import org.mockito.Mockito;
+import reactor.netty.http.server.HttpServer;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
-import org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration;
+import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
-import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
 import org.springframework.boot.web.embedded.jetty.JettyReactiveWebServerFactory;
 import org.springframework.boot.web.embedded.jetty.JettyServerCustomizer;
-import org.springframework.boot.web.embedded.jetty.JettyServletWebServerFactory;
 import org.springframework.boot.web.embedded.tomcat.TomcatConnectorCustomizer;
 import org.springframework.boot.web.embedded.tomcat.TomcatContextCustomizer;
 import org.springframework.boot.web.embedded.tomcat.TomcatProtocolHandlerCustomizer;
@@ -33,13 +34,11 @@ import org.springframework.boot.web.embedded.tomcat.TomcatReactiveWebServerFacto
 import org.springframework.boot.web.embedded.undertow.UndertowBuilderCustomizer;
 import org.springframework.boot.web.embedded.undertow.UndertowDeploymentInfoCustomizer;
 import org.springframework.boot.web.embedded.undertow.UndertowReactiveWebServerFactory;
-import org.springframework.boot.web.embedded.undertow.UndertowServletWebServerFactory;
 import org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebApplicationContext;
 import org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext;
 import org.springframework.boot.web.reactive.server.ConfigurableReactiveWebServerFactory;
 import org.springframework.boot.web.reactive.server.ReactiveWebServerFactory;
 import org.springframework.boot.web.server.WebServerFactoryCustomizer;
-import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
 import org.springframework.context.ApplicationContextException;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -161,44 +160,55 @@ public class ReactiveWebServerFactoryAutoConfigurationTests {
 
 	@Test
 	public void jettyServerCustomizerBeanIsAddedToFactory() {
-		ReactiveWebApplicationContextRunner runner = new ReactiveWebApplicationContextRunner(
+		new ReactiveWebApplicationContextRunner(
 				AnnotationConfigReactiveWebApplicationContext::new)
 						.withConfiguration(AutoConfigurations
 								.of(ReactiveWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(JettyServerCustomizer.class);
-		runner.run((context) -> {
-			JettyReactiveWebServerFactory factory = context
-					.getBean(JettyReactiveWebServerFactory.class);
-			assertThat(factory.getServerCustomizers()).hasSize(1);
-		});
+						.withClassLoader(
+								new FilteredClassLoader(Tomcat.class, HttpServer.class))
+						.withUserConfiguration(JettyServerCustomizerConfiguration.class,
+								HttpHandlerConfiguration.class)
+						.run((context) -> {
+							JettyReactiveWebServerFactory factory = context
+									.getBean(JettyReactiveWebServerFactory.class);
+							assertThat(factory.getServerCustomizers()).hasSize(1);
+						});
 	}
 
 	@Test
 	public void undertowDeploymentInfoCustomizerBeanIsAddedToFactory() {
-		ReactiveWebApplicationContextRunner runner = new ReactiveWebApplicationContextRunner(
+		new ReactiveWebApplicationContextRunner(
 				AnnotationConfigReactiveWebApplicationContext::new)
 						.withConfiguration(AutoConfigurations
 								.of(ReactiveWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(UndertowDeploymentInfoCustomizer.class);
-		runner.run((context) -> {
-			UndertowReactiveWebServerFactory factory = context
-					.getBean(UndertowReactiveWebServerFactory.class);
-			assertThat(factory.getDeploymentInfoCustomizers()).hasSize(1);
-		});
+						.withClassLoader(new FilteredClassLoader(Tomcat.class,
+								HttpServer.class, Server.class))
+						.withUserConfiguration(
+								UndertowDeploymentInfoCustomizerConfiguration.class,
+								HttpHandlerConfiguration.class)
+						.run((context) -> {
+							UndertowReactiveWebServerFactory factory = context
+									.getBean(UndertowReactiveWebServerFactory.class);
+							assertThat(factory.getDeploymentInfoCustomizers()).hasSize(1);
+						});
 	}
 
 	@Test
 	public void undertowBuilderCustomizerBeanIsAddedToFactory() {
-		ReactiveWebApplicationContextRunner runner = new ReactiveWebApplicationContextRunner(
+		new ReactiveWebApplicationContextRunner(
 				AnnotationConfigReactiveWebApplicationContext::new)
 						.withConfiguration(AutoConfigurations
 								.of(ReactiveWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(UndertowBuilderCustomizer.class);
-		runner.run((context) -> {
-			UndertowReactiveWebServerFactory factory = context
-					.getBean(UndertowReactiveWebServerFactory.class);
-			assertThat(factory.getBuilderCustomizers()).hasSize(1);
-		});
+						.withClassLoader(new FilteredClassLoader(Tomcat.class,
+								HttpServer.class, Server.class))
+						.withUserConfiguration(
+								UndertowBuilderCustomizerConfiguration.class,
+								HttpHandlerConfiguration.class)
+						.run((context) -> {
+							UndertowReactiveWebServerFactory factory = context
+									.getBean(UndertowReactiveWebServerFactory.class);
+							assertThat(factory.getBuilderCustomizers()).hasSize(1);
+						});
 	}
 
 	@Test
@@ -300,6 +310,42 @@ public class ReactiveWebServerFactoryAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class JettyServerCustomizerConfiguration {
+
+		@Bean
+		public JettyServerCustomizer protocolHandlerCustomizer() {
+			return (server) -> {
+
+			};
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class UndertowBuilderCustomizerConfiguration {
+
+		@Bean
+		public UndertowBuilderCustomizer protocolHandlerCustomizer() {
+			return (builder) -> {
+
+			};
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class UndertowDeploymentInfoCustomizerConfiguration {
+
+		@Bean
+		public UndertowDeploymentInfoCustomizer protocolHandlerCustomizer() {
+			return (deploymentInfo) -> {
+
+			};
+		}
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class ForwardedHeaderTransformerConfiguration {
 
diff --git a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java
index 87bc2131bf..d3dc810e7d 100644
--- a/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java
+++ b/spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfigurationTests.java
@@ -22,12 +22,16 @@ import javax.servlet.ServletContext;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
+import org.apache.catalina.startup.Tomcat;
+import org.eclipse.jetty.server.Server;
 import org.junit.Test;
+import reactor.netty.http.server.HttpServer;
 
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnExpression;
+import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.assertj.AssertableWebApplicationContext;
 import org.springframework.boot.test.context.runner.ContextConsumer;
 import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
@@ -39,7 +43,6 @@ import org.springframework.boot.web.embedded.tomcat.TomcatProtocolHandlerCustomi
 import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
 import org.springframework.boot.web.embedded.undertow.UndertowBuilderCustomizer;
 import org.springframework.boot.web.embedded.undertow.UndertowDeploymentInfoCustomizer;
-import org.springframework.boot.web.embedded.undertow.UndertowServletWebServer;
 import org.springframework.boot.web.embedded.undertow.UndertowServletWebServerFactory;
 import org.springframework.boot.web.server.WebServerFactoryCustomizer;
 import org.springframework.boot.web.servlet.FilterRegistrationBean;
@@ -157,9 +160,11 @@ public class ServletWebServerFactoryAutoConfigurationTests {
 	public void jettyServerCustomizerBeanIsAddedToFactory() {
 		WebApplicationContextRunner runner = new WebApplicationContextRunner(
 				AnnotationConfigServletWebServerApplicationContext::new)
+						.withClassLoader(
+								new FilteredClassLoader(Tomcat.class, HttpServer.class))
 						.withConfiguration(AutoConfigurations
 								.of(ServletWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(JettyServerCustomizer.class);
+						.withUserConfiguration(JettyServerCustomizerConfiguration.class);
 		runner.run((context) -> {
 			JettyServletWebServerFactory factory = context
 					.getBean(JettyServletWebServerFactory.class);
@@ -171,9 +176,12 @@ public class ServletWebServerFactoryAutoConfigurationTests {
 	public void undertowDeploymentInfoCustomizerBeanIsAddedToFactory() {
 		WebApplicationContextRunner runner = new WebApplicationContextRunner(
 				AnnotationConfigServletWebServerApplicationContext::new)
+						.withClassLoader(new FilteredClassLoader(Tomcat.class,
+								HttpServer.class, Server.class))
 						.withConfiguration(AutoConfigurations
 								.of(ServletWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(UndertowDeploymentInfoCustomizer.class);
+						.withUserConfiguration(
+								UndertowDeploymentInfoCustomizerConfiguration.class);
 		runner.run((context) -> {
 			UndertowServletWebServerFactory factory = context
 					.getBean(UndertowServletWebServerFactory.class);
@@ -185,9 +193,12 @@ public class ServletWebServerFactoryAutoConfigurationTests {
 	public void undertowBuilderCustomizerBeanIsAddedToFactory() {
 		WebApplicationContextRunner runner = new WebApplicationContextRunner(
 				AnnotationConfigServletWebServerApplicationContext::new)
+						.withClassLoader(new FilteredClassLoader(Tomcat.class,
+								HttpServer.class, Server.class))
 						.withConfiguration(AutoConfigurations
 								.of(ServletWebServerFactoryAutoConfiguration.class))
-						.withUserConfiguration(UndertowBuilderCustomizer.class);
+						.withUserConfiguration(
+								UndertowBuilderCustomizerConfiguration.class);
 		runner.run((context) -> {
 			UndertowServletWebServerFactory factory = context
 					.getBean(UndertowServletWebServerFactory.class);
@@ -413,6 +424,42 @@ public class ServletWebServerFactoryAutoConfigurationTests {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class JettyServerCustomizerConfiguration {
+
+		@Bean
+		public JettyServerCustomizer protocolHandlerCustomizer() {
+			return (server) -> {
+
+			};
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class UndertowBuilderCustomizerConfiguration {
+
+		@Bean
+		public UndertowBuilderCustomizer protocolHandlerCustomizer() {
+			return (builder) -> {
+
+			};
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class UndertowDeploymentInfoCustomizerConfiguration {
+
+		@Bean
+		public UndertowDeploymentInfoCustomizer protocolHandlerCustomizer() {
+			return (deploymentInfo) -> {
+
+			};
+		}
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class ForwardedHeaderFilterConfiguration {