Common constants for default AnnotationBeanNameGenerator instances

Closes gh-22591

spring-context/src/main/java/org/springframework/context/annotation/AnnotatedBeanDefinitionReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -49,7 +49,7 @@ public class AnnotatedBeanDefinitionReader {
 
 	private final BeanDefinitionRegistry registry;
 
-	private BeanNameGenerator beanNameGenerator = new AnnotationBeanNameGenerator();
+	private BeanNameGenerator beanNameGenerator = AnnotationBeanNameGenerator.INSTANCE;
 
 	private ScopeMetadataResolver scopeMetadataResolver = new AnnotationScopeMetadataResolver();
 
@@ -110,7 +110,8 @@ public class AnnotatedBeanDefinitionReader {
 	 * <p>The default is a {@link AnnotationBeanNameGenerator}.
 	 */
 	public void setBeanNameGenerator(@Nullable BeanNameGenerator beanNameGenerator) {
-		this.beanNameGenerator = (beanNameGenerator != null ? beanNameGenerator : new AnnotationBeanNameGenerator());
+		this.beanNameGenerator =
+				(beanNameGenerator != null ? beanNameGenerator : AnnotationBeanNameGenerator.INSTANCE);
 	}
 
 	/**

spring-context/src/main/java/org/springframework/context/annotation/AnnotationBeanNameGenerator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -63,6 +63,13 @@ import org.springframework.util.StringUtils;
  */
 public class AnnotationBeanNameGenerator implements BeanNameGenerator {
 
+	/**
+	 * A convenient constant for a default {@code AnnotationBeanNameGenerator} instance,
+	 * as used for component scanning purposes.
+	 * @since 5.2
+	 */
+	public static final AnnotationBeanNameGenerator INSTANCE = new AnnotationBeanNameGenerator();
+
 	private static final String COMPONENT_ANNOTATION_CLASSNAME = "org.springframework.stereotype.Component";
 
 

spring-context/src/main/java/org/springframework/context/annotation/ClassPathBeanDefinitionScanner.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -69,7 +69,7 @@ public class ClassPathBeanDefinitionScanner extends ClassPathScanningCandidateCo
 	@Nullable
 	private String[] autowireCandidatePatterns;
 
-	private BeanNameGenerator beanNameGenerator = new AnnotationBeanNameGenerator();
+	private BeanNameGenerator beanNameGenerator = AnnotationBeanNameGenerator.INSTANCE;
 
 	private ScopeMetadataResolver scopeMetadataResolver = new AnnotationScopeMetadataResolver();
 
@@ -208,7 +208,8 @@ public class ClassPathBeanDefinitionScanner extends ClassPathScanningCandidateCo
 	 * <p>Default is a {@link AnnotationBeanNameGenerator}.
 	 */
 	public void setBeanNameGenerator(@Nullable BeanNameGenerator beanNameGenerator) {
-		this.beanNameGenerator = (beanNameGenerator != null ? beanNameGenerator : new AnnotationBeanNameGenerator());
+		this.beanNameGenerator =
+				(beanNameGenerator != null ? beanNameGenerator : AnnotationBeanNameGenerator.INSTANCE);
 	}
 
 	/**

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassPostProcessor.java

@@ -86,6 +86,24 @@ import org.springframework.util.ClassUtils;
 public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
 		PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {
 
+	/**
+	 * A {@code BeanNameGenerator} using fully qualified class names as default bean names.
+	 * <p>This default for configuration-level import purposes may be overridden through
+	 * {@link #setBeanNameGenerator}. Note that the default for component scanning purposes
+	 * is a plain {@link AnnotationBeanNameGenerator#INSTANCE}, unless overridden through
+	 * {@link #setBeanNameGenerator} with a unified user-level bean name generator.
+	 * @since 5.2
+	 * @see #setBeanNameGenerator
+	 */
+	public static final AnnotationBeanNameGenerator IMPORT_BEAN_NAME_GENERATOR = new AnnotationBeanNameGenerator() {
+		@Override
+		protected String buildDefaultBeanName(BeanDefinition definition) {
+			String beanClassName = definition.getBeanClassName();
+			Assert.state(beanClassName != null, "No bean class name set");
+			return beanClassName;
+		}
+	};
+
 	private static final String IMPORT_REGISTRY_BEAN_NAME =
 			ConfigurationClassPostProcessor.class.getName() + ".importRegistry";
 
@@ -117,18 +135,11 @@ public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPo
 
 	private boolean localBeanNameGeneratorSet = false;
 
-	/* Using short class names as default bean names */
-	private BeanNameGenerator componentScanBeanNameGenerator = new AnnotationBeanNameGenerator();
+	/* Using short class names as default bean names by default. */
+	private BeanNameGenerator componentScanBeanNameGenerator = AnnotationBeanNameGenerator.INSTANCE;
 
-	/* Using fully qualified class names as default bean names */
-	private BeanNameGenerator importBeanNameGenerator = new AnnotationBeanNameGenerator() {
-		@Override
-		protected String buildDefaultBeanName(BeanDefinition definition) {
-			String beanClassName = definition.getBeanClassName();
-			Assert.state(beanClassName != null, "No bean class name set");
-			return beanClassName;
-		}
-	};
+	/* Using fully qualified class names as default bean names by default. */
+	private BeanNameGenerator importBeanNameGenerator = IMPORT_BEAN_NAME_GENERATOR;
 
 
 	@Override

spring-context/src/main/java/org/springframework/context/annotation/ImportBeanDefinitionRegistrar.java

@@ -61,9 +61,15 @@ public interface ImportBeanDefinitionRegistrar {
 	 * {@link #registerBeanDefinitions(AnnotationMetadata, BeanDefinitionRegistry)}.
 	 * @param importingClassMetadata annotation metadata of the importing class
 	 * @param registry current bean definition registry
-	 * @param importBeanNameGenerator the configuration-level bean name generator
-	 * strategy for imported beans
+	 * @param importBeanNameGenerator the bean name generator strategy for imported beans:
+	 * {@link ConfigurationClassPostProcessor#IMPORT_BEAN_NAME_GENERATOR} by default, or a
+	 * user-provided one if {@link ConfigurationClassPostProcessor#setBeanNameGenerator}
+	 * has been set. In the latter case, the passed-in strategy will be the same used for
+	 * component scanning in the containing application context (otherwise, the default
+	 * component-scan naming strategy is {@link AnnotationBeanNameGenerator#INSTANCE}).
 	 * @since 5.2
+	 * @see ConfigurationClassPostProcessor#IMPORT_BEAN_NAME_GENERATOR
+	 * @see ConfigurationClassPostProcessor#setBeanNameGenerator
 	 */
 	default void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry,
 			BeanNameGenerator importBeanNameGenerator) {