Revisit GenericApplicationContext.registerBean constructor handling

Support for Kotlin primary constructor and non-default public constructors in addition to default instantiation, aligned with AnnotationConfigApplicationContext and model attribute processing.

Issue: SPR-17292

Author: jhoeller

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

@@ -1146,14 +1146,20 @@ protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd
 			}
 		}
 
-		// Need to determine the constructor...
+		// Candidate constructors for autowiring?
 		Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
 		if (ctors != null ||
 				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
 				mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
 			return autowireConstructor(beanName, mbd, ctors, args);
 		}
 
+		// Preferred constructors for default construction?
+		ctors = mbd.getPreferredConstructors();
+		if (ctors != null) {
+			return autowireConstructor(beanName, mbd, ctors, null);
+		}
+
 		// No special handling: simply use no-arg constructor.
 		return instantiateBean(beanName, mbd);
 	}

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

@@ -17,6 +17,7 @@
 package org.springframework.beans.factory.support;
 
 import java.lang.reflect.AnnotatedElement;
+import java.lang.reflect.Constructor;
 import java.lang.reflect.Executable;
 import java.lang.reflect.Member;
 import java.lang.reflect.Method;
@@ -335,6 +336,18 @@ public ResolvableType getResolvableType() {
 		return (targetType != null ? targetType : ResolvableType.forClass(getBeanClass()));
 	}
 
+	/**
+	 * Determine preferred constructors to use for default construction, if any.
+	 * Constructor arguments will be autowired if necessary.
+	 * @return one or more preferred constructors, or {@code null} if none
+	 * (in which case the regular no-arg default constructor will be called)
+	 * @since 5.1
+	 */
+	@Nullable
+	public Constructor<?>[] getPreferredConstructors() {
+		return null;
+	}
+
 	/**
 	 * Specify a factory method name that refers to a non-overloaded method.
 	 */

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -17,19 +17,21 @@
 package org.springframework.context.support;
 
 import java.io.IOException;
+import java.lang.reflect.Constructor;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Supplier;
 
+import org.springframework.beans.BeanUtils;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.BeanDefinitionStoreException;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
 import org.springframework.beans.factory.config.AutowireCapableBeanFactory;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.BeanDefinitionCustomizer;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
-import org.springframework.beans.factory.support.BeanDefinitionBuilder;
 import org.springframework.beans.factory.support.BeanDefinitionRegistry;
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.context.ApplicationContext;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
@@ -360,9 +362,10 @@ public boolean isAlias(String beanName) {
 	 * Register a bean from the given bean class, optionally customizing its
 	 * bean definition metadata (typically declared as a lambda expression
 	 * or method reference).
-	 * @param beanClass the class of the bean
-	 * @param customizers one or more callbacks for customizing the
-	 * factory's {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
+	 * @param beanClass the class of the bean (resolving a public constructor
+	 * to be autowired, possibly simply the default constructor)
+	 * @param customizers one or more callbacks for customizing the factory's
+	 * {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
 	 * @since 5.0
 	 * @see #registerBean(String, Class, Supplier, BeanDefinitionCustomizer...)
 	 */
@@ -376,13 +379,16 @@ public final <T> void registerBean(Class<T> beanClass, BeanDefinitionCustomizer.
 	 * method reference), optionally customizing its bean definition metadata
 	 * (again typically declared as a lambda expression or method reference).
 	 * @param beanName the name of the bean (may be {@code null})
-	 * @param beanClass the class of the bean
+	 * @param beanClass the class of the bean (resolving a public constructor
+	 * to be autowired, possibly simply the default constructor)
 	 * @param customizers one or more callbacks for customizing the
 	 * factory's {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
 	 * @since 5.0
 	 * @see #registerBean(String, Class, Supplier, BeanDefinitionCustomizer...)
 	 */
-	public final <T> void registerBean(@Nullable String beanName, Class<T> beanClass, BeanDefinitionCustomizer... customizers) {
+	public final <T> void registerBean(
+			@Nullable String beanName, Class<T> beanClass, BeanDefinitionCustomizer... customizers) {
+
 		registerBean(beanName, beanClass, null, customizers);
 	}
 
@@ -393,12 +399,14 @@ public final <T> void registerBean(@Nullable String beanName, Class<T> beanClass
 	 * (again typically declared as a lambda expression or method reference).
 	 * @param beanClass the class of the bean
 	 * @param supplier a callback for creating an instance of the bean
-	 * @param customizers one or more callbacks for customizing the
-	 * factory's {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
+	 * @param customizers one or more callbacks for customizing the factory's
+	 * {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
 	 * @since 5.0
 	 * @see #registerBean(String, Class, Supplier, BeanDefinitionCustomizer...)
 	 */
-	public final <T> void registerBean(Class<T> beanClass, Supplier<T> supplier, BeanDefinitionCustomizer... customizers) {
+	public final <T> void registerBean(
+			Class<T> beanClass, Supplier<T> supplier, BeanDefinitionCustomizer... customizers) {
+
 		registerBean(null, beanClass, supplier, customizers);
 	}
 
@@ -410,22 +418,63 @@ public final <T> void registerBean(Class<T> beanClass, Supplier<T> supplier, Bea
 	 * <p>This method can be overridden to adapt the registration mechanism for
 	 * all {@code registerBean} methods (since they all delegate to this one).
 	 * @param beanName the name of the bean (may be {@code null})
-	 * @param beanClass the class of the bean (may be {@code null} if a name is given)
-	 * @param supplier a callback for creating an instance of the bean
-	 * @param customizers one or more callbacks for customizing the
-	 * factory's {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
+	 * @param beanClass the class of the bean
+	 * @param supplier a callback for creating an instance of the bean (in case
+	 * of {@code null}, resolving a public constructor to be autowired instead)
+	 * @param customizers one or more callbacks for customizing the factory's
+	 * {@link BeanDefinition}, e.g. setting a lazy-init or primary flag
 	 * @since 5.0
 	 */
-	public <T> void registerBean(@Nullable String beanName, Class<T> beanClass, @Nullable Supplier<T> supplier,
-			BeanDefinitionCustomizer... customizers) {
+	public <T> void registerBean(@Nullable String beanName, Class<T> beanClass,
+			@Nullable Supplier<T> supplier, BeanDefinitionCustomizer... customizers) {
 
-		BeanDefinitionBuilder builder = (supplier != null ?
-				BeanDefinitionBuilder.genericBeanDefinition(beanClass, supplier) :
-				BeanDefinitionBuilder.genericBeanDefinition(beanClass));
-		BeanDefinition beanDefinition = builder.applyCustomizers(customizers).getRawBeanDefinition();
+		ClassDerivedBeanDefinition beanDefinition = new ClassDerivedBeanDefinition(beanClass);
+		if (supplier != null) {
+			beanDefinition.setInstanceSupplier(supplier);
+		}
+		for (BeanDefinitionCustomizer customizer : customizers) {
+			customizer.customize(beanDefinition);
+		}
 
 		String nameToUse = (beanName != null ? beanName : beanClass.getName());
 		registerBeanDefinition(nameToUse, beanDefinition);
 	}
 
+
+	/**
+	 * {@link RootBeanDefinition} marker subclass for {@code #registerBean} based
+	 * registrations with flexible autowiring for public constructors.
+	 */
+	@SuppressWarnings("serial")
+	private static class ClassDerivedBeanDefinition extends RootBeanDefinition {
+
+		public ClassDerivedBeanDefinition(Class<?> beanClass) {
+			super(beanClass);
+		}
+
+		public ClassDerivedBeanDefinition(ClassDerivedBeanDefinition original) {
+			super(original);
+		}
+
+		@Override
+		@Nullable
+		public Constructor<?>[] getPreferredConstructors() {
+			Class<?> clazz = getBeanClass();
+			Constructor<?> primaryCtor = BeanUtils.findPrimaryConstructor(clazz);
+			if (primaryCtor != null) {
+				return new Constructor<?>[] {primaryCtor};
+			}
+			Constructor<?>[] publicCtors = clazz.getConstructors();
+			if (publicCtors.length > 0) {
+				return publicCtors;
+			}
+			return null;
+		}
+
+		@Override
+		public RootBeanDefinition cloneBeanDefinition() {
+			return new ClassDerivedBeanDefinition(this);
+		}
+	}
+
 }

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

@@ -90,6 +90,21 @@ public void getBeanByType() {
 		assertThat(testBean.name, equalTo("foo"));
 	}
 
+	@Test
+	public void getBeanByTypeRaisesNoSuchBeanDefinitionException() {
+		ApplicationContext context = new AnnotationConfigApplicationContext(Config.class);
+
+		// attempt to retrieve a bean that does not exist
+		Class<?> targetType = Pattern.class;
+		try {
+			context.getBean(targetType);
+			fail("Should have thrown NoSuchBeanDefinitionException");
+		}
+		catch (NoSuchBeanDefinitionException ex) {
+			assertThat(ex.getMessage(), containsString(format("No qualifying bean of type '%s'", targetType.getName())));
+		}
+	}
+
 	/**
 	 * Tests that Configuration classes are registered according to convention
 	 * @see org.springframework.beans.factory.support.DefaultBeanNameGenerator#generateBeanName
@@ -116,6 +131,41 @@ public void explicitConfigClassBeanNameIsRespected() {
 		assertNotNull(configObject);
 	}
 
+	@Test
+	public void autowiringIsEnabledByDefault() {
+		ApplicationContext context = new AnnotationConfigApplicationContext(AutowiredConfig.class);
+		assertThat(context.getBean(TestBean.class).name, equalTo("foo"));
+	}
+
+	@Test
+	public void nullReturningBeanPostProcessor() {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
+		context.register(AutowiredConfig.class);
+		context.getBeanFactory().addBeanPostProcessor(new BeanPostProcessor() {
+			@Override
+			public Object postProcessBeforeInitialization(Object bean, String beanName) {
+				return (bean instanceof TestBean ? null : bean);
+			}
+			@Override
+			public Object postProcessAfterInitialization(Object bean, String beanName) {
+				return bean;
+			}
+		});
+		context.getBeanFactory().addBeanPostProcessor(new BeanPostProcessor() {
+			@Override
+			public Object postProcessBeforeInitialization(Object bean, String beanName) {
+				bean.getClass().getName();
+				return bean;
+			}
+			@Override
+			public Object postProcessAfterInitialization(Object bean, String beanName) {
+				bean.getClass().getName();
+				return bean;
+			}
+		});
+		context.refresh();
+	}
+
 	@Test
 	public void individualBeans() {
 		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
@@ -299,74 +349,6 @@ public void individualBeanWithFactoryBeanSupplierAndTargetType() {
 		assertEquals(FactoryBean.class, context.getType("&fb"));
 	}
 
-	@Test
-	public void getBeanByTypeRaisesNoSuchBeanDefinitionException() {
-		ApplicationContext context = new AnnotationConfigApplicationContext(Config.class);
-
-		// attempt to retrieve a bean that does not exist
-		Class<?> targetType = Pattern.class;
-		try {
-			context.getBean(targetType);
-			fail("Should have thrown NoSuchBeanDefinitionException");
-		}
-		catch (NoSuchBeanDefinitionException ex) {
-			assertThat(ex.getMessage(), containsString(format("No qualifying bean of type '%s'", targetType.getName())));
-		}
-	}
-
-	@Test
-	public void getBeanByTypeAmbiguityRaisesException() {
-		ApplicationContext context = new AnnotationConfigApplicationContext(TwoTestBeanConfig.class);
-
-		try {
-			context.getBean(TestBean.class);
-		}
-		catch (NoSuchBeanDefinitionException ex) {
-			assertThat(ex.getMessage(),
-					allOf(
-						containsString("No qualifying bean of type '" + TestBean.class.getName() + "'"),
-						containsString("tb1"),
-						containsString("tb2")
-					)
-				);
-		}
-	}
-
-	@Test
-	public void autowiringIsEnabledByDefault() {
-		ApplicationContext context = new AnnotationConfigApplicationContext(AutowiredConfig.class);
-		assertThat(context.getBean(TestBean.class).name, equalTo("foo"));
-	}
-
-	@Test
-	public void nullReturningBeanPostProcessor() {
-		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
-		context.register(AutowiredConfig.class);
-		context.getBeanFactory().addBeanPostProcessor(new BeanPostProcessor() {
-			@Override
-			public Object postProcessBeforeInitialization(Object bean, String beanName) {
-				return (bean instanceof TestBean ? null : bean);
-			}
-			@Override
-			public Object postProcessAfterInitialization(Object bean, String beanName) {
-				return bean;
-			}
-		});
-		context.getBeanFactory().addBeanPostProcessor(new BeanPostProcessor() {
-			@Override
-			public Object postProcessBeforeInitialization(Object bean, String beanName) {
-				bean.getClass().getName();
-				return bean;
-			}
-			@Override
-			public Object postProcessAfterInitialization(Object bean, String beanName) {
-				bean.getClass().getName();
-				return bean;
-			}
-		});
-		context.refresh();
-	}
-
 
 	@Configuration
 	static class Config {