Configuration classes can opt into lite mode (proxyBeanMethods=false)

Closes gh-22461

Author: jhoeller

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -344,9 +344,9 @@
  *
  * <p>By default, {@code @Bean} methods will be <em>eagerly instantiated</em> at container
  * bootstrap time.  To avoid this, {@code @Configuration} may be used in conjunction with
- * the {@link Lazy @Lazy} annotation to indicate that all {@code @Bean} methods declared within
- * the class are by default lazily initialized. Note that {@code @Lazy} may be used on
- * individual {@code @Bean} methods as well.
+ * the {@link Lazy @Lazy} annotation to indicate that all {@code @Bean} methods declared
+ * within the class are by default lazily initialized. Note that {@code @Lazy} may be used
+ * on individual {@code @Bean} methods as well.
  *
  * <h2>Testing support for {@code @Configuration} classes</h2>
  *
@@ -391,7 +391,9 @@
  * <ul>
  * <li>Configuration classes must be provided as classes (i.e. not as instances returned
  * from factory methods), allowing for runtime enhancements through a generated subclass.
- * <li>Configuration classes must be non-final.
+ * <li>Configuration classes must be non-final (allowing for subclasses at runtime),
+ * unless the {@link #proxyBeanMethods() proxyBeanMethods} flag is set to {@code false}
+ * in which case no runtime-generated subclass is necessary.
  * <li>Configuration classes must be non-local (i.e. may not be declared within a method).
  * <li>Any nested configuration classes must be declared as {@code static}.
  * <li>{@code @Bean} methods may not in turn create further configuration classes
@@ -401,6 +403,7 @@
  *
  * @author Rod Johnson
  * @author Chris Beams
+ * @author Juergen Hoeller
  * @since 3.0
  * @see Bean
  * @see Profile
@@ -435,4 +438,25 @@
 	@AliasFor(annotation = Component.class)
 	String value() default "";
 
+	/**
+	 * Specify whether {@code @Bean} methods should get proxied in order to enforce
+	 * bean lifecycle behavior, e.g. to return shared singleton bean instances even
+	 * in case of direct {@code @Bean} method calls in user code. This feature
+	 * requires method interception, implemented through a runtime-generated CGLIB
+	 * subclass which comes with limitations such as the configuration class and
+	 * its methods not being allowed to declare {@code final}.
+	 * <p>The default is {@code true}, allowing for 'inter-bean references' within
+	 * the configuration class as well as for external calls to this configuration's
+	 * {@code @Bean} methods, e.g. from another configuration class. If this is not
+	 * needed since each of this particular configuration's {@code @Bean} methods
+	 * is self-contained and designed as a plain factory method for container use,
+	 * switch this flag to {@code false} in order to avoid CGLIB subclass processing.
+	 * <p>Turning off bean method interception effectively processes {@code @Bean}
+	 * methods individually like when declared on non-{@code @Configuration} classes,
+	 * a.k.a. "@Bean Lite Mode" (see {@link Bean @Bean's javadoc}). It is therefore
+	 * behaviorally equivalent to removing the {@code @Configuration} stereotype.
+	 * @since 5.2
+	 */
+	boolean proxyBeanMethods() default true;
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -112,10 +112,11 @@ else if (beanDef instanceof AbstractBeanDefinition && ((AbstractBeanDefinition)
 			}
 		}
 
-		if (isFullConfigurationCandidate(metadata)) {
+		Map<String, Object> config = metadata.getAnnotationAttributes(Configuration.class.getName());
+		if (config != null && !Boolean.FALSE.equals(config.get("proxyBeanMethods"))) {
 			beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
 		}
-		else if (isLiteConfigurationCandidate(metadata)) {
+		else if (config != null || isConfigurationCandidate(metadata)) {
 			beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
 		}
 		else {
@@ -135,33 +136,10 @@ else if (isLiteConfigurationCandidate(metadata)) {
 	 * Check the given metadata for a configuration class candidate
 	 * (or nested component class declared within a configuration/component class).
 	 * @param metadata the metadata of the annotated class
-	 * @return {@code true} if the given class is to be registered as a
-	 * reflection-detected bean definition; {@code false} otherwise
+	 * @return {@code true} if the given class is to be registered for
+	 * configuration class processing; {@code false} otherwise
 	 */
 	public static boolean isConfigurationCandidate(AnnotationMetadata metadata) {
-		return (isFullConfigurationCandidate(metadata) || isLiteConfigurationCandidate(metadata));
-	}
-
-	/**
-	 * Check the given metadata for a full configuration class candidate
-	 * (i.e. a class annotated with {@code @Configuration}).
-	 * @param metadata the metadata of the annotated class
-	 * @return {@code true} if the given class is to be processed as a full
-	 * configuration class, including cross-method call interception
-	 */
-	public static boolean isFullConfigurationCandidate(AnnotationMetadata metadata) {
-		return metadata.isAnnotated(Configuration.class.getName());
-	}
-
-	/**
-	 * Check the given metadata for a lite configuration class candidate
-	 * (e.g. a class annotated with {@code @Component} or just having
-	 * {@code @Import} declarations or {@code @Bean methods}).
-	 * @param metadata the metadata of the annotated class
-	 * @return {@code true} if the given class is to be processed as a lite
-	 * configuration class, just registering it and scanning it for {@code @Bean} methods
-	 */
-	public static boolean isLiteConfigurationCandidate(AnnotationMetadata metadata) {
 		// Do not consider an interface or an annotation...
 		if (metadata.isInterface()) {
 			return false;

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

@@ -90,8 +90,7 @@ public void setup() {
 	 * <p>Technically, {@link ConfigurationClassPostProcessor} could fail to enhance the
 	 * registered Configuration classes and many use cases would still work.
 	 * Certain cases, however, like inter-bean singleton references would not.
-	 * We test for such a case below, and in doing so prove that enhancement is
-	 * working.
+	 * We test for such a case below, and in doing so prove that enhancement is working.
 	 */
 	@Test
 	public void enhancementIsPresentBecauseSingletonSemanticsAreRespected() {
@@ -104,6 +103,16 @@ public void enhancementIsPresentBecauseSingletonSemanticsAreRespected() {
 		assertTrue(Arrays.asList(beanFactory.getDependentBeans("foo")).contains("bar"));
 	}
 
+	@Test
+	public void enhancementIsNotPresentForProxyBeanMethodsFlagSetToFalse() {
+		beanFactory.registerBeanDefinition("config", new RootBeanDefinition(NonEnhancedSingletonBeanConfig.class));
+		ConfigurationClassPostProcessor pp = new ConfigurationClassPostProcessor();
+		pp.postProcessBeanFactory(beanFactory);
+		Foo foo = beanFactory.getBean("foo", Foo.class);
+		Bar bar = beanFactory.getBean("bar", Bar.class);
+		assertNotSame(foo, bar.foo);
+	}
+
 	@Test
 	public void configurationIntrospectionOfInnerClassesWorksWithDotNameSyntax() {
 		beanFactory.registerBeanDefinition("config", new RootBeanDefinition(getClass().getName() + ".SingletonBeanConfig"));
@@ -115,8 +124,8 @@ public void configurationIntrospectionOfInnerClassesWorksWithDotNameSyntax() {
 	}
 
 	/**
-	 * Tests the fix for SPR-5655, a special workaround that prefers reflection
-	 * over ASM if a bean class is already loaded.
+	 * Tests the fix for SPR-5655, a special workaround that prefers reflection over ASM
+	 * if a bean class is already loaded.
 	 */
 	@Test
 	public void alreadyLoadedConfigurationClasses() {
@@ -129,8 +138,7 @@ public void alreadyLoadedConfigurationClasses() {
 	}
 
 	/**
-	 * Tests whether a bean definition without a specified bean class is handled
-	 * correctly.
+	 * Tests whether a bean definition without a specified bean class is handled correctly.
 	 */
 	@Test
 	public void postProcessorIntrospectsInheritedDefinitionsCorrectly() {
@@ -1070,6 +1078,18 @@ static class SingletonBeanConfig {
 		}
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	static class NonEnhancedSingletonBeanConfig {
+
+		public @Bean Foo foo() {
+			return new Foo();
+		}
+
+		public @Bean Bar bar() {
+			return new Bar(foo());
+		}
+	}
+
 	@Configuration
 	@Order(2)
 	static class OverridingSingletonBeanConfig {