Introduce AutowireCandidateResolver.cloneIfNecessary() method

Closes gh-25131

Author: jhoeller

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.beans.factory.support;
 
+import org.springframework.beans.BeanUtils;
 import org.springframework.beans.factory.config.BeanDefinitionHolder;
 import org.springframework.beans.factory.config.DependencyDescriptor;
 import org.springframework.lang.Nullable;
@@ -99,4 +100,22 @@ default Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor
 		return null;
 	}
 
+	/**
+	 * Return a clone of this resolver instance if necessary, retaining its local
+	 * configuration and allowing for the cloned instance to get associated with
+	 * a new bean factory, or this original instance if there is no such state.
+	 * <p>The default implementation creates a separate instance via the default
+	 * class constructor, assuming no specific configuration state to copy.
+	 * Subclasses may override this with custom configuration state handling
+	 * or with standard {@link Cloneable} support (as implemented by Spring's
+	 * own configurable {@code AutowireCandidateResolver} variants), or simply
+	 * return {@code this} (as in {@link SimpleAutowireCandidateResolver}).
+	 * @since 5.2.7
+	 * @see GenericTypeAwareAutowireCandidateResolver#cloneIfNecessary()
+	 * @see DefaultListableBeanFactory#copyConfigurationFrom
+	 */
+	default AutowireCandidateResolver cloneIfNecessary() {
+		return BeanUtils.instantiateClass(getClass());
+	}
+
 }

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

@@ -46,7 +46,6 @@
 
 import javax.inject.Provider;
 
-import org.springframework.beans.BeanUtils;
 import org.springframework.beans.BeansException;
 import org.springframework.beans.TypeConverter;
 import org.springframework.beans.factory.BeanCreationException;
@@ -157,7 +156,7 @@ public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFacto
 	private Comparator<Object> dependencyComparator;
 
 	/** Resolver to use for checking if a bean definition is an autowire candidate. */
-	private AutowireCandidateResolver autowireCandidateResolver = new SimpleAutowireCandidateResolver();
+	private AutowireCandidateResolver autowireCandidateResolver = SimpleAutowireCandidateResolver.INSTANCE;
 
 	/** Map from dependency type to corresponding autowired value. */
 	private final Map<Class<?>, Object> resolvableDependencies = new ConcurrentHashMap<>(16);
@@ -328,8 +327,7 @@ public void copyConfigurationFrom(ConfigurableBeanFactory otherFactory) {
 			this.allowEagerClassLoading = otherListableFactory.allowEagerClassLoading;
 			this.dependencyComparator = otherListableFactory.dependencyComparator;
 			// A clone of the AutowireCandidateResolver since it is potentially BeanFactoryAware...
-			setAutowireCandidateResolver(
-					BeanUtils.instantiateClass(otherListableFactory.getAutowireCandidateResolver().getClass()));
+			setAutowireCandidateResolver(otherListableFactory.getAutowireCandidateResolver().cloneIfNecessary());
 			// Make resolvable dependencies (e.g. ResourceLoader) available here as well...
 			this.resolvableDependencies.putAll(otherListableFactory.resolvableDependencies);
 		}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -43,7 +43,7 @@
  * @since 4.0
  */
 public class GenericTypeAwareAutowireCandidateResolver extends SimpleAutowireCandidateResolver
-		implements BeanFactoryAware {
+		implements BeanFactoryAware, Cloneable {
 
 	@Nullable
 	private BeanFactory beanFactory;
@@ -177,4 +177,21 @@ protected ResolvableType getReturnTypeForFactoryMethod(RootBeanDefinition rbd, D
 		return null;
 	}
 
+
+	/**
+	 * This implementation clones all instance fields through standard
+	 * {@link Cloneable} support, allowing for subsequent reconfiguration
+	 * of the cloned instance through a fresh {@link #setBeanFactory} call.
+	 * @see #clone()
+	 */
+	@Override
+	public AutowireCandidateResolver cloneIfNecessary() {
+		try {
+			return (AutowireCandidateResolver) clone();
+		}
+		catch (CloneNotSupportedException ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -30,6 +30,13 @@
  */
 public class SimpleAutowireCandidateResolver implements AutowireCandidateResolver {
 
+	/**
+	 * Shared instance of {@code SimpleAutowireCandidateResolver}.
+	 * @since 5.2.7
+	 */
+	public static final SimpleAutowireCandidateResolver INSTANCE = new SimpleAutowireCandidateResolver();
+
+
 	@Override
 	public boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
 		return bdHolder.getBeanDefinition().isAutowireCandidate();
@@ -40,6 +47,11 @@ public boolean isRequired(DependencyDescriptor descriptor) {
 		return descriptor.isRequired();
 	}
 
+	@Override
+	public boolean hasQualifier(DependencyDescriptor descriptor) {
+		return false;
+	}
+
 	@Override
 	@Nullable
 	public Object getSuggestedValue(DependencyDescriptor descriptor) {
@@ -52,4 +64,13 @@ public Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor,
 		return null;
 	}
 
+	/**
+	 * This implementation returns {@code this} as-is.
+	 * @see #INSTANCE
+	 */
+	@Override
+	public AutowireCandidateResolver cloneIfNecessary() {
+		return this;
+	}
+
 }