Consistent handling of NullBean instances in resolveNamedBean

Closes gh-26271

Author: jhoeller

spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractBeanFactory.java

@@ -250,7 +250,7 @@ protected <T> T doGetBean(
 			throws BeansException {
 
 		String beanName = transformedBeanName(name);
-		Object bean;
+		Object beanInstance;
 
 		// Eagerly check singleton cache for manually registered singletons.
 		Object sharedInstance = getSingleton(beanName);
@@ -264,7 +264,7 @@ protected <T> T doGetBean(
 					logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
 				}
 			}
-			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
+			beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, null);
 		}
 
 		else {
@@ -342,7 +342,7 @@ else if (requiredType != null) {
 							throw ex;
 						}
 					});
-					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
+					beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
 				}
 
 				else if (mbd.isPrototype()) {
@@ -355,7 +355,7 @@ else if (mbd.isPrototype()) {
 					finally {
 						afterPrototypeCreation(beanName);
 					}
-					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
+					beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
 				}
 
 				else {
@@ -377,7 +377,7 @@ else if (mbd.isPrototype()) {
 								afterPrototypeCreation(beanName);
 							}
 						});
-						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
+						beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
 					}
 					catch (IllegalStateException ex) {
 						throw new ScopeNotActiveException(beanName, scopeName, ex);
@@ -395,14 +395,19 @@ else if (mbd.isPrototype()) {
 			}
 		}
 
+		return adaptBeanInstance(name, beanInstance, requiredType);
+	}
+
+	@SuppressWarnings("unchecked")
+	<T> T adaptBeanInstance(String name, Object bean, @Nullable Class<?> requiredType) {
 		// Check if required type matches the type of the actual bean instance.
 		if (requiredType != null && !requiredType.isInstance(bean)) {
 			try {
-				T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
+				Object convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
 				if (convertedBean == null) {
 					throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
 				}
-				return convertedBean;
+				return (T) convertedBean;
 			}
 			catch (TypeMismatchException ex) {
 				if (logger.isTraceEnabled()) {

spring-beans/src/main/java/org/springframework/beans/factory/support/DefaultListableBeanFactory.java

@@ -1231,8 +1231,7 @@ private <T> NamedBeanHolder<T> resolveNamedBean(
 		}
 
 		if (candidateNames.length == 1) {
-			String beanName = candidateNames[0];
-			return new NamedBeanHolder<>(beanName, (T) getBean(beanName, requiredType.toClass(), args));
+			return resolveNamedBean(candidateNames[0], requiredType, args);
 		}
 		else if (candidateNames.length > 1) {
 			Map<String, Object> candidates = CollectionUtils.newLinkedHashMap(candidateNames.length);
@@ -1251,8 +1250,11 @@ else if (candidateNames.length > 1) {
 			}
 			if (candidateName != null) {
 				Object beanInstance = candidates.get(candidateName);
-				if (beanInstance == null || beanInstance instanceof Class) {
-					beanInstance = getBean(candidateName, requiredType.toClass(), args);
+				if (beanInstance == null) {
+					return null;
+				}
+				if (beanInstance instanceof Class) {
+					return resolveNamedBean(candidateName, requiredType, args);
 				}
 				return new NamedBeanHolder<>(candidateName, (T) beanInstance);
 			}
@@ -1264,6 +1266,17 @@ else if (candidateNames.length > 1) {
 		return null;
 	}
 
+	@Nullable
+	private <T> NamedBeanHolder<T> resolveNamedBean(
+			String beanName, ResolvableType requiredType, @Nullable Object[] args) throws BeansException {
+
+		Object bean = getBean(beanName, null, args);
+		if (bean instanceof NullBean) {
+			return null;
+		}
+		return new NamedBeanHolder<T>(beanName, adaptBeanInstance(beanName, bean, requiredType.toClass()));
+	}
+
 	@Override
 	@Nullable
 	public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,

spring-context/src/test/java/org/springframework/context/annotation/AnnotationConfigApplicationContextTests.java

@@ -271,9 +271,15 @@ void individualBeanWithNullReturningSupplier() {
 		assertThat(ObjectUtils.containsElement(context.getBeanNamesForType(BeanA.class), "a")).isTrue();
 		assertThat(ObjectUtils.containsElement(context.getBeanNamesForType(BeanB.class), "b")).isTrue();
 		assertThat(ObjectUtils.containsElement(context.getBeanNamesForType(BeanC.class), "c")).isTrue();
+
 		assertThat(context.getBeansOfType(BeanA.class)).isEmpty();
 		assertThat(context.getBeansOfType(BeanB.class).values().iterator().next()).isSameAs(context.getBean(BeanB.class));
 		assertThat(context.getBeansOfType(BeanC.class).values().iterator().next()).isSameAs(context.getBean(BeanC.class));
+
+		assertThatExceptionOfType(NoSuchBeanDefinitionException.class).isThrownBy(() ->
+				context.getBeanFactory().resolveNamedBean(BeanA.class));
+		assertThat(context.getBeanFactory().resolveNamedBean(BeanB.class).getBeanInstance()).isSameAs(context.getBean(BeanB.class));
+		assertThat(context.getBeanFactory().resolveNamedBean(BeanC.class).getBeanInstance()).isSameAs(context.getBean(BeanC.class));
 	}
 
 	@Test