Fix package tangle caused by ApplicationContextFactory

Fix package tangle by changing `ApplicationContextFactory.DEFAULT` to
use `spring.factories` to discover implementations rather than needing
direct access to our own `ApplicationContext` classes.

Closes gh-30272

Author: philwebb

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/ApplicationContextFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -19,10 +19,9 @@
 import java.util.function.Supplier;
 
 import org.springframework.beans.BeanUtils;
-import org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext;
-import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.core.io.support.SpringFactoriesLoader;
 
 /**
  * Strategy interface for creating the {@link ConfigurableApplicationContext} used by a
@@ -43,14 +42,14 @@ public interface ApplicationContextFactory {
 	 */
 	ApplicationContextFactory DEFAULT = (webApplicationType) -> {
 		try {
-			switch (webApplicationType) {
-			case SERVLET:
-				return new AnnotationConfigServletWebServerApplicationContext();
-			case REACTIVE:
-				return new AnnotationConfigReactiveWebServerApplicationContext();
-			default:
-				return new AnnotationConfigApplicationContext();
+			for (ApplicationContextFactory candidate : SpringFactoriesLoader
+					.loadFactories(ApplicationContextFactory.class, ApplicationContextFactory.class.getClassLoader())) {
+				ConfigurableApplicationContext context = candidate.create(webApplicationType);
+				if (context != null) {
+					return context;
+				}
 			}
+			return new AnnotationConfigApplicationContext();
 		}
 		catch (Exception ex) {
 			throw new IllegalStateException("Unable create a default ApplicationContext instance, "

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/reactive/context/AnnotationConfigReactiveWebServerApplicationContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -23,6 +23,9 @@
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.support.BeanNameGenerator;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.boot.ApplicationContextFactory;
+import org.springframework.boot.WebApplicationType;
+import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.AnnotatedBeanDefinitionReader;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.AnnotationConfigRegistry;
@@ -209,4 +212,18 @@ protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactor
 		}
 	}
 
+	/**
+	 * {@link ApplicationContextFactory} registered in {@code spring.factories} to support
+	 * {@link AnnotationConfigReactiveWebServerApplicationContext}.
+	 */
+	static class Factory implements ApplicationContextFactory {
+
+		@Override
+		public ConfigurableApplicationContext create(WebApplicationType webApplicationType) {
+			return (webApplicationType != WebApplicationType.REACTIVE) ? null
+					: new AnnotationConfigReactiveWebServerApplicationContext();
+		}
+
+	}
+
 }

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/servlet/context/AnnotationConfigServletWebServerApplicationContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2022 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.
@@ -23,6 +23,9 @@
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.support.BeanNameGenerator;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.boot.ApplicationContextFactory;
+import org.springframework.boot.WebApplicationType;
+import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.AnnotatedBeanDefinitionReader;
 import org.springframework.context.annotation.AnnotationConfigRegistry;
 import org.springframework.context.annotation.AnnotationConfigUtils;
@@ -206,4 +209,18 @@ protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactor
 		}
 	}
 
+	/**
+	 * {@link ApplicationContextFactory} registered in {@code spring.factories} to support
+	 * {@link AnnotationConfigServletWebServerApplicationContext}.
+	 */
+	static class Factory implements ApplicationContextFactory {
+
+		@Override
+		public ConfigurableApplicationContext create(WebApplicationType webApplicationType) {
+			return (webApplicationType != WebApplicationType.SERVLET) ? null
+					: new AnnotationConfigServletWebServerApplicationContext();
+		}
+
+	}
+
 }

spring-boot-project/spring-boot/src/main/resources/META-INF/spring.factories

@@ -19,6 +19,11 @@ org.springframework.boot.context.config.ConfigDataLoader=\
 org.springframework.boot.context.config.ConfigTreeConfigDataLoader,\
 org.springframework.boot.context.config.StandardConfigDataLoader
 
+# Application Context Factories
+org.springframework.boot.ApplicationContextFactory=\
+org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext.Factory,\
+org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext.Factory
+
 # Run Listeners
 org.springframework.boot.SpringApplicationRunListener=\
 org.springframework.boot.context.event.EventPublishingRunListener