Improve target detection for FactoryBeans with generic

Closes gh-28809

spring-beans/src/main/java/org/springframework/beans/factory/aot/DefaultBeanRegistrationCodeFragments.java

@@ -72,23 +72,45 @@ class DefaultBeanRegistrationCodeFragments extends BeanRegistrationCodeFragments
 	public Class<?> getTarget(RegisteredBean registeredBean,
 			Executable constructorOrFactoryMethod) {
 
-		Class<?> target = extractDeclaringClass(constructorOrFactoryMethod);
+		Class<?> target = extractDeclaringClass(registeredBean.getBeanType(),
+				constructorOrFactoryMethod);
 		while (target.getName().startsWith("java.") && registeredBean.isInnerBean()) {
 			target = registeredBean.getParent().getBeanClass();
 		}
 		return target;
 	}
 
-	private Class<?> extractDeclaringClass(Executable executable) {
+	private Class<?> extractDeclaringClass(ResolvableType beanType, Executable executable) {
 		Class<?> declaringClass = ClassUtils.getUserClass(executable.getDeclaringClass());
 		if (executable instanceof Constructor<?>
 				&& AccessVisibility.forMember(executable) == AccessVisibility.PUBLIC
 				&& FactoryBean.class.isAssignableFrom(declaringClass)) {
-			return ResolvableType.forType(declaringClass).as(FactoryBean.class).getGeneric(0).toClass();
+			return extractTargetClassFromFactoryBean(declaringClass, beanType);
 		}
 		return executable.getDeclaringClass();
 	}
 
+	/**
+	 * Extract the target class of a public {@link FactoryBean} based on its
+	 * constructor. If the implementation does not resolve the target class
+	 * because it itself uses a generic, attempt to extract it from the
+	 * bean type.
+	 * @param factoryBeanType the factory bean type
+	 * @param beanType the bean type
+	 * @return the target class to use
+	 */
+	private Class<?> extractTargetClassFromFactoryBean(Class<?> factoryBeanType, ResolvableType beanType) {
+		ResolvableType target = ResolvableType.forType(factoryBeanType)
+				.as(FactoryBean.class).getGeneric(0);
+		if (target.getType().equals(Class.class)) {
+			return target.toClass();
+		}
+		else if (factoryBeanType.isAssignableFrom(beanType.toClass())) {
+			return beanType.as(FactoryBean.class).getGeneric(0).toClass();
+		}
+		return beanType.toClass();
+	}
+
 	@Override
 	public CodeBlock generateNewBeanDefinitionCode(GenerationContext generationContext,
 			ResolvableType beanType, BeanRegistrationCode beanRegistrationCode) {

spring-beans/src/test/java/org/springframework/beans/factory/aot/DefaultBeanRegistrationCodeFragmentsTests.java

@@ -27,6 +27,7 @@
 import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.beans.testfixture.beans.factory.DummyFactory;
 import org.springframework.beans.testfixture.beans.factory.aot.MockBeanRegistrationsCode;
+import org.springframework.core.ResolvableType;
 import org.springframework.core.testfixture.aot.generate.TestGenerationContext;
 import org.springframework.util.ReflectionUtils;
 
@@ -57,6 +58,29 @@ void getTargetOnConstructorToPublicFactoryBean() {
 				SimpleBeanFactoryBean.class.getDeclaredConstructors()[0])).isEqualTo(SimpleBean.class);
 	}
 
+	@Test
+	void getTargetOnConstructorToPublicGenericFactoryBeanExtractTargetFromFactoryBeanType() {
+		RegisteredBean registeredBean = registerTestBean(ResolvableType
+				.forClassWithGenerics(GenericFactoryBean.class, SimpleBean.class));
+		assertThat(createInstance(registeredBean).getTarget(registeredBean,
+				GenericFactoryBean.class.getDeclaredConstructors()[0])).isEqualTo(SimpleBean.class);
+	}
+
+	@Test
+	void getTargetOnConstructorToPublicGenericFactoryBeanWithBoundExtractTargetFromFactoryBeanType() {
+		RegisteredBean registeredBean = registerTestBean(ResolvableType
+				.forClassWithGenerics(NumberFactoryBean.class, Integer.class));
+		assertThat(createInstance(registeredBean).getTarget(registeredBean,
+				NumberFactoryBean.class.getDeclaredConstructors()[0])).isEqualTo(Integer.class);
+	}
+
+	@Test
+	void getTargetOnConstructorToPublicGenericFactoryBeanUseBeanTypeAsFallback() {
+		RegisteredBean registeredBean = registerTestBean(SimpleBean.class);
+		assertThat(createInstance(registeredBean).getTarget(registeredBean,
+				GenericFactoryBean.class.getDeclaredConstructors()[0])).isEqualTo(SimpleBean.class);
+	}
+
 	@Test
 	void getTargetOnConstructorToProtectedFactoryBean() {
 		RegisteredBean registeredBean = registerTestBean(SimpleBean.class);
@@ -138,6 +162,12 @@ private RegisteredBean registerTestBean(Class<?> beanType) {
 		return RegisteredBean.of(this.beanFactory, "testBean");
 	}
 
+	private RegisteredBean registerTestBean(ResolvableType beanType) {
+		this.beanFactory.registerBeanDefinition("testBean",
+				new RootBeanDefinition(beanType));
+		return RegisteredBean.of(this.beanFactory, "testBean");
+	}
+
 	private BeanRegistrationCodeFragments createInstance(RegisteredBean registeredBean) {
 		return new DefaultBeanRegistrationCodeFragments(this.beanRegistrationsCode, registeredBean,
 				new BeanDefinitionMethodGeneratorFactory(this.beanFactory));

spring-beans/src/testFixtures/java/org/springframework/beans/factory/aot/GenericFactoryBean.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2002-2022 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.beans.factory.aot;
+
+import org.springframework.beans.BeanUtils;
+import org.springframework.beans.factory.FactoryBean;
+import org.springframework.lang.Nullable;
+
+/**
+ * A public {@link FactoryBean} with a generic type.
+ *
+ * @author Stephane Nicoll
+ */
+public class GenericFactoryBean<T> implements FactoryBean<T> {
+
+	private final Class<T> beanType;
+
+	public GenericFactoryBean(Class<T> beanType) {
+		this.beanType = beanType;
+	}
+
+	@Nullable
+	@Override
+	public T getObject() throws Exception {
+		return BeanUtils.instantiateClass(this.beanType);
+	}
+
+	@Nullable
+	@Override
+	public Class<?> getObjectType() {
+		return this.beanType;
+	}
+}

spring-beans/src/testFixtures/java/org/springframework/beans/factory/aot/NumberFactoryBean.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2002-2022 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.beans.factory.aot;
+
+/**
+ * A {@link GenericFactoryBean} that has a bound for the target type.
+ *
+ * @author Stephane Nicoll
+ */
+public class NumberFactoryBean<T extends Number> extends GenericFactoryBean<T> {
+
+	public NumberFactoryBean(Class<T> beanType) {
+		super(beanType);
+	}
+
+}

spring-beans/src/testFixtures/java/org/springframework/beans/factory/aot/SimpleBeanFactoryBean.java

@@ -19,20 +19,14 @@
 import org.springframework.beans.factory.FactoryBean;
 
 /**
- * A public {@link FactoryBean}.
+ * A public {@link FactoryBean} with a resolved generic for {@link GenericFactoryBean}.
  *
  * @author Stephane Nicoll
  */
-public class SimpleBeanFactoryBean implements FactoryBean<SimpleBean> {
+public class SimpleBeanFactoryBean extends GenericFactoryBean<SimpleBean> {
 
-	@Override
-	public SimpleBean getObject() throws Exception {
-		return new SimpleBean();
-	}
-
-	@Override
-	public Class<?> getObjectType() {
-		return SimpleBean.class;
+	public SimpleBeanFactoryBean() {
+		super(SimpleBean.class);
 	}
 
 }