Custom resolution of preferred constructors for createBean(Class)

Avoids side effects of traditional AUTOWIRE_CONSTRUCTOR algorithm.

Closes gh-30041

Author: jhoeller

spring-beans/src/main/java/org/springframework/beans/BeanUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -246,7 +246,8 @@ public static <T> Constructor<T> getResolvableConstructor(Class<T> clazz) {
 			// A single public constructor
 			return (Constructor<T>) ctors[0];
 		}
-		else if (ctors.length == 0){
+		else if (ctors.length == 0) {
+			// No public constructors -> check non-public
 			ctors = clazz.getDeclaredConstructors();
 			if (ctors.length == 1) {
 				// A single non-public constructor, e.g. from a non-public record type

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

@@ -130,10 +130,10 @@ public interface AutowireCapableBeanFactory extends BeanFactory {
 	 * {@link BeanPostProcessor BeanPostProcessors}.
 	 * <p>Note: This is intended for creating a fresh instance, populating annotated
 	 * fields and methods as well as applying all standard bean initialization callbacks.
-	 * Constructor resolution is done via {@link #AUTOWIRE_CONSTRUCTOR}, also influenced
-	 * by {@link SmartInstantiationAwareBeanPostProcessor#determineCandidateConstructors}.
-	 * It does <i>not</i> imply traditional by-name or by-type autowiring of properties;
-	 * use {@link #createBean(Class, int, boolean)} for those purposes.
+	 * Constructor resolution is based on Kotlin primary / single public / single non-public,
+	 * with a fallback to the default constructor in ambiguous scenarios, also influenced
+	 * by {@link SmartInstantiationAwareBeanPostProcessor#determineCandidateConstructors}
+	 * (e.g. for annotation-driven constructor selection).
 	 * @param beanClass the class of the bean to create
 	 * @return the new bean instance
 	 * @throws BeansException if instantiation or wiring failed

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

@@ -315,8 +315,7 @@ public void copyConfigurationFrom(ConfigurableBeanFactory otherFactory) {
 	@SuppressWarnings("unchecked")
 	public <T> T createBean(Class<T> beanClass) throws BeansException {
 		// Use non-singleton bean definition, to avoid registering bean as dependent bean.
-		RootBeanDefinition bd = new RootBeanDefinition(beanClass);
-		bd.setAutowireMode(AUTOWIRE_CONSTRUCTOR);
+		RootBeanDefinition bd = new CreateFromClassBeanDefinition(beanClass);
 		bd.setScope(SCOPE_PROTOTYPE);
 		bd.allowCaching = ClassUtils.isCacheSafe(beanClass, getBeanClassLoader());
 		return (T) createBean(beanClass.getName(), bd, null);
@@ -1909,6 +1908,36 @@ Log getLogger() {
 	}
 
 
+	/**
+	 * {@link RootBeanDefinition} subclass for {@code #createBean} calls with
+	 * flexible selection of a Kotlin primary / single public / single non-public
+	 * constructor candidate in addition to the default constructor.
+	 * @see BeanUtils#getResolvableConstructor(Class)
+	 */
+	@SuppressWarnings("serial")
+	private static class CreateFromClassBeanDefinition extends RootBeanDefinition {
+
+		public CreateFromClassBeanDefinition(Class<?> beanClass) {
+			super(beanClass);
+		}
+
+		public CreateFromClassBeanDefinition(CreateFromClassBeanDefinition original) {
+			super(original);
+		}
+
+		@Override
+		@Nullable
+		public Constructor<?>[] getPreferredConstructors() {
+			return ConstructorResolver.determinePreferredConstructors(getBeanClass());
+		}
+
+		@Override
+		public RootBeanDefinition cloneBeanDefinition() {
+			return new CreateFromClassBeanDefinition(this);
+		}
+	}
+
+
 	/**
 	 * Special DependencyDescriptor variant for Spring's good old autowire="byType" mode.
 	 * Always optional; never considering the parameter name for choosing a primary candidate.
@@ -1941,7 +1970,7 @@ private static class FactoryBeanMethodTypeFinder implements MethodCallback {
 		}
 
 		@Override
-		public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
+		public void doWith(Method method) throws IllegalArgumentException {
 			if (isFactoryBeanMethod(method)) {
 				ResolvableType returnType = ResolvableType.forMethodReturnType(method);
 				ResolvableType candidate = returnType.as(FactoryBean.class).getGeneric();

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

@@ -1222,6 +1222,54 @@ static InjectionPoint setCurrentInjectionPoint(@Nullable InjectionPoint injectio
 		return old;
 	}
 
+	/**
+	 * See {@link BeanUtils#getResolvableConstructor(Class)} for alignment.
+	 * This variant adds a lenient fallback to the default constructor if available, similar to
+	 * {@link org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor#determineCandidateConstructors}.
+	 */
+	@Nullable
+	static Constructor<?>[] determinePreferredConstructors(Class<?> clazz) {
+		Constructor<?> primaryCtor = BeanUtils.findPrimaryConstructor(clazz);
+
+		Constructor<?> defaultCtor;
+		try {
+			defaultCtor = clazz.getDeclaredConstructor();
+		}
+		catch (NoSuchMethodException ex) {
+			defaultCtor = null;
+		}
+
+		if (primaryCtor != null) {
+			if (defaultCtor != null && !primaryCtor.equals(defaultCtor)) {
+				return new Constructor<?>[] {primaryCtor, defaultCtor};
+			}
+			else {
+				return new Constructor<?>[] {primaryCtor};
+			}
+		}
+
+		Constructor<?>[] ctors = clazz.getConstructors();
+		if (ctors.length == 1) {
+			// A single public constructor, potentially in combination with a non-public default constructor
+			if (defaultCtor != null && !ctors[0].equals(defaultCtor)) {
+				return new Constructor<?>[] {ctors[0], defaultCtor};
+			}
+			else {
+				return ctors;
+			}
+		}
+		else if (ctors.length == 0) {
+			// No public constructors -> check non-public
+			ctors = clazz.getDeclaredConstructors();
+			if (ctors.length == 1) {
+				// A single non-public constructor, e.g. from a non-public record type
+				return ctors;
+			}
+		}
+
+		return null;
+	}
+
 
 	/**
 	 * Private inner class for holding argument combinations.

spring-beans/src/test/java/org/springframework/beans/factory/DefaultListableBeanFactoryTests.java

@@ -2126,6 +2126,23 @@ void createBeanWithDisposableBean() {
 		assertThat(tb.wasDestroyed()).isTrue();
 	}
 
+	@Test
+	void createBeanWithNonDefaultConstructor() {
+		lbf.registerBeanDefinition("otherTestBean", new RootBeanDefinition(TestBean.class));
+		TestBeanRecipient tb = lbf.createBean(TestBeanRecipient.class);
+		assertThat(lbf.containsSingleton("otherTestBean")).isTrue();
+		assertThat(tb.testBean).isEqualTo(lbf.getBean("otherTestBean"));
+		lbf.destroyBean(tb);
+	}
+
+	@Test
+	void createBeanWithPreferredDefaultConstructor() {
+		lbf.registerBeanDefinition("otherTestBean", new RootBeanDefinition(TestBean.class));
+		TestBean tb = lbf.createBean(TestBean.class);
+		assertThat(lbf.containsSingleton("otherTestBean")).isFalse();
+		lbf.destroyBean(tb);
+	}
+
 	@Test
 	void configureBean() {
 		MutablePropertyValues pvs = new MutablePropertyValues();

spring-context-support/src/main/java/org/springframework/scheduling/quartz/SpringBeanJobFactory.java

@@ -22,6 +22,7 @@
 import org.springframework.beans.BeanWrapper;
 import org.springframework.beans.MutablePropertyValues;
 import org.springframework.beans.PropertyAccessorFactory;
+import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
 import org.springframework.lang.Nullable;
@@ -86,8 +87,9 @@ public void setSchedulerContext(SchedulerContext schedulerContext) {
 	@Override
 	protected Object createJobInstance(TriggerFiredBundle bundle) throws Exception {
 		Object job = (this.applicationContext != null ?
+				// to be replaced with createBean(Class) in 6.1
 				this.applicationContext.getAutowireCapableBeanFactory().createBean(
-						bundle.getJobDetail().getJobClass()) :
+						bundle.getJobDetail().getJobClass(), AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR, false) :
 				super.createJobInstance(bundle));
 
 		if (isEligibleForPropertyPopulation(job)) {

spring-context/src/main/java/org/springframework/context/support/GenericApplicationContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -558,7 +558,7 @@ public <T> void registerBean(@Nullable String beanName, Class<T> beanClass,
 
 
 	/**
-	 * {@link RootBeanDefinition} marker subclass for {@code #registerBean} based
+	 * {@link RootBeanDefinition} subclass for {@code #registerBean} based
 	 * registrations with flexible autowiring for public constructors.
 	 */
 	@SuppressWarnings("serial")

spring-orm/src/main/java/org/springframework/orm/hibernate5/SpringBeanContainer.java

@@ -144,7 +144,7 @@ private SpringContainedBean<?> createBean(
 		try {
 			if (lifecycleOptions.useJpaCompliantCreation()) {
 				return new SpringContainedBean<>(
-						this.beanFactory.createBean(beanType),
+						this.beanFactory.createBean(beanType, AutowireCapableBeanFactory.AUTOWIRE_CONSTRUCTOR, false),
 						this.beanFactory::destroyBean);
 			}
 			else {