Do not cache prototype @ControllerAdvice beans

Spring Framework 5.2 introduced support for caching @ControllerAdvice
beans; however, this caching was also applied incorrectly to
non-singleton beans.

This commit addresses this regression by only caching singleton
@ControllerAdvice beans.

Closes gh-24157

spring-web/src/main/java/org/springframework/web/method/ControllerAdviceBean.java

@@ -54,6 +54,7 @@ public class ControllerAdviceBean implements Ordered {
 	 */
 	private final Object beanOrName;
 
+	private final boolean isSingletonBean;
 	/**
 	 * Reference to the resolved bean instance, potentially lazily retrieved
 	 * via the {@code BeanFactory}.
@@ -84,6 +85,7 @@ public class ControllerAdviceBean implements Ordered {
 		this.beanType = ClassUtils.getUserClass(bean.getClass());
 		this.beanTypePredicate = createBeanTypePredicate(this.beanType);
 		this.beanFactory = null;
+		this.isSingletonBean = true;
 	}
 
 	/**
@@ -115,6 +117,7 @@ public class ControllerAdviceBean implements Ordered {
 				"] does not contain specified controller advice bean '" + beanName + "'");
 
 		this.beanOrName = beanName;
+		this.isSingletonBean = beanFactory.isSingleton(beanName);
 		this.beanType = getBeanType(beanName, beanFactory);
 		this.beanTypePredicate = (controllerAdvice != null ? createBeanTypePredicate(controllerAdvice) :
 				createBeanTypePredicate(this.beanType));
@@ -191,7 +194,7 @@ public class ControllerAdviceBean implements Ordered {
 	 * will be cached, thereby avoiding repeated lookups in the {@code BeanFactory}.
 	 */
 	public Object resolveBean() {
-		if (this.resolvedBean == null) {
+		if (!this.isSingletonBean || this.resolvedBean == null) {
 			// this.beanOrName must be a String representing the bean name if
 			// this.resolvedBean is null.
 			this.resolvedBean = obtainBeanFactory().getBean((String) this.beanOrName);