Exclude SmartInitializingSingletones from lazy initialization

Fixes gh-26470

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

@@ -16,10 +16,12 @@
 
 package org.springframework.boot;
 
+import java.util.ArrayList;
 import java.util.Collection;
 
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.beans.factory.SmartInitializingSingleton;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
@@ -30,6 +32,11 @@ import org.springframework.core.Ordered;
  * {@link BeanFactoryPostProcessor} to set lazy-init on bean definitions that are not
  * {@link LazyInitializationExcludeFilter excluded} and have not already had a value
  * explicitly set.
+ * <p>
+ * Note that {@link SmartInitializingSingleton SmartInitializingSingletons} are
+ * automatically excluded from lazy initialization to ensure that their
+ * {@link SmartInitializingSingleton#afterSingletonsInstantiated() callback method} is
+ * invoked.
  *
  * @author Andy Wilkinson
  * @author Madhura Bhave
@@ -42,9 +49,7 @@ public final class LazyInitializationBeanFactoryPostProcessor implements BeanFac
 
 	@Override
 	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
-		// Take care not to force the eager init of factory beans when getting filters
-		Collection<LazyInitializationExcludeFilter> filters = beanFactory
-				.getBeansOfType(LazyInitializationExcludeFilter.class, false, false).values();
+		Collection<LazyInitializationExcludeFilter> filters = getFilters(beanFactory);
 		for (String beanName : beanFactory.getBeanDefinitionNames()) {
 			BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);
 			if (beanDefinition instanceof AbstractBeanDefinition) {
@@ -53,6 +58,14 @@ public final class LazyInitializationBeanFactoryPostProcessor implements BeanFac
 		}
 	}
 
+	private Collection<LazyInitializationExcludeFilter> getFilters(ConfigurableListableBeanFactory beanFactory) {
+		// Take care not to force the eager init of factory beans when getting filters
+		ArrayList<LazyInitializationExcludeFilter> filters = new ArrayList<>(
+				beanFactory.getBeansOfType(LazyInitializationExcludeFilter.class, false, false).values());
+		filters.add(LazyInitializationExcludeFilter.forBeanTypes(SmartInitializingSingleton.class));
+		return filters;
+	}
+
 	private void postProcess(ConfigurableListableBeanFactory beanFactory,
 			Collection<LazyInitializationExcludeFilter> filters, String beanName,
 			AbstractBeanDefinition beanDefinition) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/LazyInitializationBeanFactoryPostProcessorTests.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2012-2021 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.SmartInitializingSingleton;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link LazyInitializationBeanFactoryPostProcessor}.
+ *
+ * @author Andy Wilkinson
+ */
+class LazyInitializationBeanFactoryPostProcessorTests {
+
+	@Test
+	void whenLazyInitializationIsEnabledThenNormalBeansAreNotInitializedUntilRequired() {
+		try (AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext()) {
+			context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
+			context.register(BeanState.class, ExampleBean.class);
+			context.refresh();
+			BeanState beanState = context.getBean(BeanState.class);
+			assertThat(beanState.initializedBeans).isEmpty();
+			context.getBean(ExampleBean.class);
+			assertThat(beanState.initializedBeans).containsExactly(ExampleBean.class);
+		}
+	}
+
+	@Test
+	void whenLazyInitializationIsEnabledThenSmartInitializingSingletonsAreInitializedDuringRefresh() {
+		try (AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext()) {
+			context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
+			context.register(BeanState.class, ExampleSmartInitializingSingleton.class);
+			context.refresh();
+			BeanState beanState = context.getBean(BeanState.class);
+			assertThat(beanState.initializedBeans).containsExactly(ExampleSmartInitializingSingleton.class);
+			assertThat(context.getBean(ExampleSmartInitializingSingleton.class).callbackInvoked).isTrue();
+		}
+	}
+
+	static class ExampleBean {
+
+		ExampleBean(BeanState beanState) {
+			beanState.initializedBeans.add(getClass());
+		}
+
+	}
+
+	static class ExampleSmartInitializingSingleton implements SmartInitializingSingleton {
+
+		private boolean callbackInvoked;
+
+		ExampleSmartInitializingSingleton(BeanState beanState) {
+			beanState.initializedBeans.add(getClass());
+		}
+
+		@Override
+		public void afterSingletonsInstantiated() {
+			this.callbackInvoked = true;
+		}
+
+	}
+
+	static class BeanState {
+
+		private final List<Class<?>> initializedBeans = new ArrayList<>();
+
+	}
+
+}