Avoid reflection when creating manual RootBeanDefinitions

Closes gh-22318

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/ReactiveWebServerFactoryAutoConfiguration.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.autoconfigure.web.reactive;
 
+import java.util.function.Supplier;
+
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
@@ -100,12 +102,14 @@ public class ReactiveWebServerFactoryAutoConfiguration {
 				return;
 			}
 			registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor",
-					WebServerFactoryCustomizerBeanPostProcessor.class);
+					WebServerFactoryCustomizerBeanPostProcessor.class,
+					WebServerFactoryCustomizerBeanPostProcessor::new);
 		}
 
-		private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name, Class<?> beanClass) {
+		private <T> void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name,
+				Class<T> beanClass, Supplier<T> instanceSupplier) {
 			if (ObjectUtils.isEmpty(this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
-				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
+				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass, instanceSupplier);
 				beanDefinition.setSynthetic(true);
 				registry.registerBeanDefinition(name, beanDefinition);
 			}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/ServletWebServerFactoryAutoConfiguration.java

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.autoconfigure.web.servlet;
 
+import java.util.function.Supplier;
+
 import javax.servlet.DispatcherType;
 import javax.servlet.ServletRequest;
 
@@ -111,14 +113,16 @@ public class ServletWebServerFactoryAutoConfiguration {
 				return;
 			}
 			registerSyntheticBeanIfMissing(registry, "webServerFactoryCustomizerBeanPostProcessor",
-					WebServerFactoryCustomizerBeanPostProcessor.class);
+					WebServerFactoryCustomizerBeanPostProcessor.class,
+					WebServerFactoryCustomizerBeanPostProcessor::new);
 			registerSyntheticBeanIfMissing(registry, "errorPageRegistrarBeanPostProcessor",
-					ErrorPageRegistrarBeanPostProcessor.class);
+					ErrorPageRegistrarBeanPostProcessor.class, ErrorPageRegistrarBeanPostProcessor::new);
 		}
 
-		private void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name, Class<?> beanClass) {
+		private <T> void registerSyntheticBeanIfMissing(BeanDefinitionRegistry registry, String name,
+				Class<T> beanClass, Supplier<T> instanceSupplier) {
 			if (ObjectUtils.isEmpty(this.beanFactory.getBeanNamesForType(beanClass, true, false))) {
-				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass);
+				RootBeanDefinition beanDefinition = new RootBeanDefinition(beanClass, instanceSupplier);
 				beanDefinition.setSynthetic(true);
 				registry.registerBeanDefinition(name, beanDefinition);
 			}