Enforce non-null value from getBean and at injection points

Bean-derived null values may still get passed into bean properties and injection points but only if those are declared as non-required. Note that getBean will never return null; a manual bean.equals(null) / "null".equals(bean.toString()) check identifies expected null values now.  This will only ever happen with custom FactoryBeans or factory methods returning null - and since all common cases are handled by autowiring or bean property values in bean definitions, there should be no need to ever manually check for such a null value received from getBean.

Issue: SPR-15829

Author: jhoeller

spring-beans/src/main/java/org/springframework/beans/factory/ObjectFactory.java

@@ -45,7 +45,6 @@ public interface ObjectFactory<T> {
 	 * @return the resulting instance
 	 * @throws BeansException in case of creation errors
 	 */
-	@Nullable
 	T getObject() throws BeansException;
 
 }

spring-beans/src/main/java/org/springframework/beans/factory/ObjectProvider.java

@@ -40,7 +40,6 @@ public interface ObjectProvider<T> extends ObjectFactory<T> {
 	 * @throws BeansException in case of creation errors
 	 * @see #getObject()
 	 */
-	@Nullable
 	T getObject(Object... args) throws BeansException;
 
 	/**

spring-beans/src/main/java/org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessor.java

@@ -725,7 +725,7 @@ public ShortcutDependencyDescriptor(DependencyDescriptor original, String shortc
 
 		@Override
 		public Object resolveShortcut(BeanFactory beanFactory) {
-			return resolveCandidate(this.shortcut, this.requiredType, beanFactory);
+			return beanFactory.getBean(this.shortcut, this.requiredType);
 		}
 	}
 

spring-beans/src/main/java/org/springframework/beans/factory/config/AutowireCapableBeanFactory.java

@@ -268,7 +268,6 @@ void autowireBeanProperties(Object existingBean, int autowireMode, boolean depen
 	 * @return the bean instance to use, either the original or a wrapped one
 	 * @throws BeansException if the initialization failed
 	 */
-	@Nullable
 	Object initializeBean(Object existingBean, String beanName) throws BeansException;
 
 	/**
@@ -281,7 +280,6 @@ void autowireBeanProperties(Object existingBean, int autowireMode, boolean depen
 	 * @throws BeansException if any post-processing failed
 	 * @see BeanPostProcessor#postProcessBeforeInitialization
 	 */
-	@Nullable
 	Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
 			throws BeansException;
 
@@ -295,7 +293,6 @@ Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String b
 	 * @throws BeansException if any post-processing failed
 	 * @see BeanPostProcessor#postProcessAfterInitialization
 	 */
-	@Nullable
 	Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
 			throws BeansException;
 

spring-beans/src/main/java/org/springframework/beans/factory/config/DependencyDescriptor.java

@@ -252,7 +252,7 @@ public Object resolveShortcut(BeanFactory beanFactory) throws BeansException {
 	public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory)
 			throws BeansException {
 
-		return beanFactory.getBean(beanName, requiredType);
+		return beanFactory.getBean(beanName);
 	}
 
 

spring-beans/src/main/java/org/springframework/beans/factory/config/SmartInstantiationAwareBeanPostProcessor.java

@@ -87,7 +87,6 @@ default Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, Stri
 	 * (typically with the passed-in bean instance as default)
 	 * @throws org.springframework.beans.BeansException in case of errors
 	 */
-	@Nullable
 	default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
 		return bean;
 	}

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

@@ -410,37 +410,36 @@ public void applyBeanPropertyValues(Object existingBean, String beanName) throws
 	}
 
 	@Override
-	@Nullable
 	public Object initializeBean(Object existingBean, String beanName) {
 		return initializeBean(beanName, existingBean, null);
 	}
 
 	@Override
-	@Nullable
 	public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
 			throws BeansException {
 
 		Object result = existingBean;
 		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
-			result = beanProcessor.postProcessBeforeInitialization(result, beanName);
-			if (result == null) {
-				return null;
+			Object current = beanProcessor.postProcessBeforeInitialization(result, beanName);
+			if (current == null) {
+				return result;
 			}
+			result = current;
 		}
 		return result;
 	}
 
 	@Override
-	@Nullable
 	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
 			throws BeansException {
 
 		Object result = existingBean;
 		for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
-			result = beanProcessor.postProcessAfterInitialization(result, beanName);
-			if (result == null) {
-				return null;
+			Object current = beanProcessor.postProcessAfterInitialization(result, beanName);
+			if (current == null) {
+				return result;
 			}
+			result = current;
 		}
 		return result;
 	}
@@ -461,7 +460,6 @@ public void destroyBean(Object existingBean) {
 	 * @see #doCreateBean
 	 */
 	@Override
-	@Nullable
 	protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
 			throws BeanCreationException {
 
@@ -535,7 +533,6 @@ protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable O
 	 * @see #instantiateUsingFactoryMethod
 	 * @see #autowireConstructor
 	 */
-	@Nullable
 	protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
 			throws BeanCreationException {
 
@@ -547,23 +544,23 @@ protected Object doCreateBean(final String beanName, final RootBeanDefinition mb
 		if (instanceWrapper == null) {
 			instanceWrapper = createBeanInstance(beanName, mbd, args);
 		}
-		final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
-		Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
-		mbd.resolvedTargetType = beanType;
+		final Object bean = instanceWrapper.getWrappedInstance();
+		Class<?> beanType = instanceWrapper.getWrappedClass();
+		if (beanType != NullBean.class) {
+			mbd.resolvedTargetType = beanType;
+		}
 
-		if (beanType != null) {
-			// Allow post-processors to modify the merged bean definition.
-			synchronized (mbd.postProcessingLock) {
-				if (!mbd.postProcessed) {
-					try {
-						applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
-					}
-					catch (Throwable ex) {
-						throw new BeanCreationException(mbd.getResourceDescription(), beanName,
-								"Post-processing of merged bean definition failed", ex);
-					}
-					mbd.postProcessed = true;
+		// Allow post-processors to modify the merged bean definition.
+		synchronized (mbd.postProcessingLock) {
+			if (!mbd.postProcessed) {
+				try {
+					applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
 				}
+				catch (Throwable ex) {
+					throw new BeanCreationException(mbd.getResourceDescription(), beanName,
+							"Post-processing of merged bean definition failed", ex);
+				}
+				mbd.postProcessed = true;
 			}
 		}
 
@@ -583,9 +580,7 @@ protected Object doCreateBean(final String beanName, final RootBeanDefinition mb
 		Object exposedObject = bean;
 		try {
 			populateBean(beanName, mbd, instanceWrapper);
-			if (exposedObject != null) {
-				exposedObject = initializeBean(beanName, exposedObject, mbd);
-			}
+			exposedObject = initializeBean(beanName, exposedObject, mbd);
 		}
 		catch (Throwable ex) {
 			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
@@ -624,15 +619,13 @@ else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
 			}
 		}
 
-		if (bean != null) {
-			// Register bean as disposable.
-			try {
-				registerDisposableBeanIfNecessary(beanName, bean, mbd);
-			}
-			catch (BeanDefinitionValidationException ex) {
-				throw new BeanCreationException(
-						mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
-			}
+		// Register bean as disposable.
+		try {
+			registerDisposableBeanIfNecessary(beanName, bean, mbd);
+		}
+		catch (BeanDefinitionValidationException ex) {
+			throw new BeanCreationException(
+					mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
 		}
 
 		return exposedObject;
@@ -904,17 +897,13 @@ class Holder { @Nullable Class<?> value = null; }
 	 * @param bean the raw bean instance
 	 * @return the object to expose as bean reference
 	 */
-	@Nullable
-	protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, @Nullable Object bean) {
+	protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
 		Object exposedObject = bean;
-		if (bean != null && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
+		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
 			for (BeanPostProcessor bp : getBeanPostProcessors()) {
 				if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
 					SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
 					exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
-					if (exposedObject == null) {
-						return null;
-					}
 				}
 			}
 		}
@@ -954,9 +943,6 @@ private FactoryBean<?> getSingletonFactoryBeanForTypeCheck(String beanName, Root
 				instance = resolveBeforeInstantiation(beanName, mbd);
 				if (instance == null) {
 					bw = createBeanInstance(beanName, mbd, null);
-					if (bw == null) {
-						return null;
-					}
 					instance = bw.getWrappedInstance();
 				}
 			}
@@ -995,9 +981,6 @@ private FactoryBean<?> getNonSingletonFactoryBeanForTypeCheck(String beanName, R
 			instance = resolveBeforeInstantiation(beanName, mbd);
 			if (instance == null) {
 				BeanWrapper bw = createBeanInstance(beanName, mbd, null);
-				if (bw == null) {
-					return null;
-				}
 				instance = bw.getWrappedInstance();
 			}
 		}
@@ -1097,7 +1080,6 @@ protected Object applyBeanPostProcessorsBeforeInstantiation(Class<?> beanClass,
 	 * @see #autowireConstructor
 	 * @see #instantiateBean
 	 */
-	@Nullable
 	protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
 		// Make sure bean class is actually resolved at this point.
 		Class<?> beanClass = resolveBeanClass(mbd, beanName);
@@ -1184,9 +1166,8 @@ protected BeanWrapper obtainFromSupplier(Supplier<?> instanceSupplier, String be
 	 * @see #obtainFromSupplier
 	 */
 	@Override
-	@Nullable
 	protected Object getObjectForBeanInstance(
-			@Nullable Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
+			Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
 
 		String currentlyCreatedBean = this.currentlyCreatedBean.get();
 		if (currentlyCreatedBean != null) {
@@ -1262,7 +1243,6 @@ protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefin
 	 * @return a BeanWrapper for the new instance
 	 * @see #getBean(String, Object[])
 	 */
-	@Nullable
 	protected BeanWrapper instantiateUsingFactoryMethod(
 			String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) {
 
@@ -1698,7 +1678,6 @@ private Object convertForProperty(Object value, String propertyName, BeanWrapper
 	 * @see #invokeInitMethods
 	 * @see #applyBeanPostProcessorsAfterInitialization
 	 */
-	@Nullable
 	protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
 		if (System.getSecurityManager() != null) {
 			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
@@ -1715,18 +1694,16 @@ protected Object initializeBean(final String beanName, final Object bean, @Nulla
 			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
 		}
 
-		if (wrappedBean != null) {
-			try {
-				invokeInitMethods(beanName, wrappedBean, mbd);
-			}
-			catch (Throwable ex) {
-				throw new BeanCreationException(
-						(mbd != null ? mbd.getResourceDescription() : null),
-						beanName, "Invocation of init method failed", ex);
-			}
-			if (mbd == null || !mbd.isSynthetic()) {
-				wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
-			}
+		try {
+			invokeInitMethods(beanName, wrappedBean, mbd);
+		}
+		catch (Throwable ex) {
+			throw new BeanCreationException(
+					(mbd != null ? mbd.getResourceDescription() : null),
+					beanName, "Invocation of init method failed", ex);
+		}
+		if (mbd == null || !mbd.isSynthetic()) {
+			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
 		}
 
 		return wrappedBean;

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

@@ -380,9 +380,13 @@ else if (mbd.isPrototype()) {
 		// corner cases, in particular in functional configuration and Kotlin scenarios.
 		// A future Spring generation might eventually forbid null values completely
 		// and throw IllegalStateExceptions instead of leniently passing them through.
-		if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
+		if (requiredType != null && !requiredType.isInstance(bean)) {
 			try {
-				return getTypeConverter().convertIfNecessary(bean, requiredType);
+				T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
+				if (convertedBean == null) {
+					throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
+				}
+				return convertedBean;
 			}
 			catch (TypeMismatchException ex) {
 				if (logger.isDebugEnabled()) {
@@ -421,9 +425,6 @@ public boolean isSingleton(String name) throws NoSuchBeanDefinitionException {
 				return !BeanFactoryUtils.isFactoryDereference(name);
 			}
 		}
-		else if (containsSingleton(beanName)) {
-			return true;
-		}
 
 		// No singleton instance found -> check bean definition.
 		BeanFactory parentBeanFactory = getParentBeanFactory();
@@ -496,7 +497,7 @@ public boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuc
 
 		// Check manually registered singletons.
 		Object beanInstance = getSingleton(beanName, false);
-		if (beanInstance != null) {
+		if (beanInstance != null && beanInstance.getClass() != NullBean.class) {
 			if (beanInstance instanceof FactoryBean) {
 				if (!BeanFactoryUtils.isFactoryDereference(name)) {
 					Class<?> type = getTypeForFactoryBean((FactoryBean<?>) beanInstance);
@@ -605,18 +606,14 @@ public Class<?> getType(String name) throws NoSuchBeanDefinitionException {
 
 		// Check manually registered singletons.
 		Object beanInstance = getSingleton(beanName, false);
-		if (beanInstance != null) {
+		if (beanInstance != null && beanInstance.getClass() != NullBean.class) {
 			if (beanInstance instanceof FactoryBean && !BeanFactoryUtils.isFactoryDereference(name)) {
 				return getTypeForFactoryBean((FactoryBean<?>) beanInstance);
 			}
 			else {
 				return beanInstance.getClass();
 			}
 		}
-		else if (containsSingleton(beanName) && !containsBeanDefinition(beanName)) {
-			// null instance registered
-			return null;
-		}
 
 		// No singleton instance found -> check bean definition.
 		BeanFactory parentBeanFactory = getParentBeanFactory();
@@ -1014,10 +1011,6 @@ public boolean isFactoryBean(String name) throws NoSuchBeanDefinitionException {
 		if (beanInstance != null) {
 			return (beanInstance instanceof FactoryBean);
 		}
-		else if (containsSingleton(beanName)) {
-			// null instance registered
-			return false;
-		}
 
 		// No singleton instance found -> check bean definition.
 		if (!containsBeanDefinition(beanName) && getParentBeanFactory() instanceof ConfigurableBeanFactory) {
@@ -1631,13 +1624,8 @@ protected boolean hasBeanCreationStarted() {
 	 * @param mbd the merged bean definition
 	 * @return the object to expose for the bean
 	 */
-	@Nullable
 	protected Object getObjectForBeanInstance(
-			@Nullable Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
-
-		if (beanInstance == null) {
-			return null;
-		}
+			Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
 
 		// Don't let calling code try to dereference the factory if the bean isn't a factory.
 		if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
@@ -1782,7 +1770,6 @@ protected void registerDisposableBeanIfNecessary(String beanName, Object bean, R
 	 * @return a new instance of the bean
 	 * @throws BeanCreationException if the bean could not be created
 	 */
-	@Nullable
 	protected abstract Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
 			throws BeanCreationException;