Deprecate refresh(ApplicationContext) and add refresh(ConfigurableAC)

refresh can only ever be called with a ConfigurableApplicationContext
and we want to evolve the refresh API to reflect that. This commit
takes the first step by overloading refresh(ApplicationContext) with
a new refresh(ConfigurationApplicationContext) method and deprecating
refresh(ApplicationContext). Where the call to refresh is made, the
argument is cast to ApplicationContext to ensure that
refresh(ApplicationContext) is called. This ensures that any existing
override of the method is still effective.

Closes gh-18519

Author: wilkinsona

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

@@ -394,7 +394,7 @@ private void prepareContext(ConfigurableApplicationContext context, Configurable
 	}
 
 	private void refreshContext(ConfigurableApplicationContext context) {
-		refresh(context);
+		refresh((ApplicationContext) context);
 		if (this.registerShutdownHook) {
 			try {
 				context.registerShutdownHook();
@@ -741,10 +741,21 @@ protected BeanDefinitionLoader createBeanDefinitionLoader(BeanDefinitionRegistry
 	/**
 	 * Refresh the underlying {@link ApplicationContext}.
 	 * @param applicationContext the application context to refresh
+	 * @deprecated since 2.3.0 in favor of
+	 * {@link #refresh(ConfigurableApplicationContext)}
 	 */
+	@Deprecated
 	protected void refresh(ApplicationContext applicationContext) {
-		Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
-		((AbstractApplicationContext) applicationContext).refresh();
+		Assert.isInstanceOf(ConfigurableApplicationContext.class, applicationContext);
+		refresh((ConfigurableApplicationContext) applicationContext);
+	}
+
+	/**
+	 * Refresh the underlying {@link ApplicationContext}.
+	 * @param applicationContext the application context to refresh
+	 */
+	protected void refresh(ConfigurableApplicationContext applicationContext) {
+		applicationContext.refresh();
 	}
 
 	/**