1.@Configuration注解介绍

在spring中是通过ConfigurationClassPostProcessor来处理@Configuration注解的。

1.1 容器注入ConfigurationClassPostProcessor后置处理器

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AnnotationConfigUtils#registerAnnotationConfigProcessors(): 注册注解后置处理器。

	public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(BeanDefinitionRegistry registry, @Nullable Object source) {DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);if (beanFactory != null) {if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);}if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());}}Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));}if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));}// Check for Jakarta Annotations support, and if present add the CommonAnnotationBeanPostProcessor.if (jakartaAnnotationsPresent && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));}// Check for JSR-250 support, and if present add an InitDestroyAnnotationBeanPostProcessor// for the javax variant of PostConstruct/PreDestroy.if (jsr250Present && !registry.containsBeanDefinition(JSR250_ANNOTATION_PROCESSOR_BEAN_NAME)) {try {RootBeanDefinition def = new RootBeanDefinition(InitDestroyAnnotationBeanPostProcessor.class);def.getPropertyValues().add("initAnnotationType", classLoader.loadClass("javax.annotation.PostConstruct"));def.getPropertyValues().add("destroyAnnotationType", classLoader.loadClass("javax.annotation.PreDestroy"));def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, JSR250_ANNOTATION_PROCESSOR_BEAN_NAME));}catch (ClassNotFoundException ex) {// Failed to load javax variants of the annotation types -> ignore.}}// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition();try {def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,AnnotationConfigUtils.class.getClassLoader()));}catch (ClassNotFoundException ex) {throw new IllegalStateException("Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);}def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));}if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));}if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);def.setSource(source);beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));}return beanDefs;}

向容器注入了ConfigurationClassPostProcessor, AutowiredAnnotationBeanPostProcessor, CommonAnnotationBeanPostProcessor, PersistenceAnnotationBeanPostProcessor,EventListenerMethodProcessor, DefaultEventListenerFactory后置处理器。

1.2 ConfigurationClassPostProcessor介绍

BeanDefinitionRegistryPostProcessor:

在bean定义文件注册表标准初始化完成后修改内部bean 定义文件.所有的bean定义文件都会被加载,但是bean还没有被实例化.这就允许在下一步的前置处理阶段开始前,继续添加bean的定义文件。

ConfigurationClassPostProcessor 在 refresh#invokeBeanFactoryPostProcessors() 方法中触发方法。

PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors():

触发了ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry方法。

2.ConfigurationClassPostProcessor解析

ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry():

1. 前面的校验是判断是否处理过该BeanDefinitionRegistry
2. processConfigBeanDefinitions方法为处理配置类的Bean

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {List<BeanDefinitionHolder> configCandidates = new ArrayList<>();String[] candidateNames = registry.getBeanDefinitionNames();for (String beanName : candidateNames) {BeanDefinition beanDef = registry.getBeanDefinition(beanName);if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {if (logger.isDebugEnabled()) {logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);}}else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));}}// Return immediately if no @Configuration classes were foundif (configCandidates.isEmpty()) {return;}// Sort by previously determined @Order value, if applicableconfigCandidates.sort((bd1, bd2) -> {int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());return Integer.compare(i1, i2);});// Detect any custom bean name generation strategy supplied through the enclosing application contextSingletonBeanRegistry sbr = null;if (registry instanceof SingletonBeanRegistry) {sbr = (SingletonBeanRegistry) registry;if (!this.localBeanNameGeneratorSet) {BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR);if (generator != null) {this.componentScanBeanNameGenerator = generator;this.importBeanNameGenerator = generator;}}}if (this.environment == null) {this.environment = new StandardEnvironment();}// Parse each @Configuration classConfigurationClassParser parser = new ConfigurationClassParser(this.metadataReaderFactory, this.problemReporter, this.environment,this.resourceLoader, this.componentScanBeanNameGenerator, registry);Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());do {parser.parse(candidates);parser.validate();Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());configClasses.removeAll(alreadyParsed);// Read the model and create bean definitions based on its contentif (this.reader == null) {this.reader = new ConfigurationClassBeanDefinitionReader(registry, this.sourceExtractor, this.resourceLoader, this.environment,this.importBeanNameGenerator, parser.getImportRegistry());}this.reader.loadBeanDefinitions(configClasses);alreadyParsed.addAll(configClasses);candidates.clear();if (registry.getBeanDefinitionCount() > candidateNames.length) {String[] newCandidateNames = registry.getBeanDefinitionNames();Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));Set<String> alreadyParsedClasses = new HashSet<>();for (ConfigurationClass configurationClass : alreadyParsed) {alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());}for (String candidateName : newCandidateNames) {if (!oldCandidateNames.contains(candidateName)) {BeanDefinition bd = registry.getBeanDefinition(candidateName);if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&!alreadyParsedClasses.contains(bd.getBeanClassName())) {candidates.add(new BeanDefinitionHolder(bd, candidateName));}}}candidateNames = newCandidateNames;}}while (!candidates.isEmpty());// Register the ImportRegistry as a bean in order to support ImportAware @Configuration classesif (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());}if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) {// Clear cache in externally provided MetadataReaderFactory; this is a no-op// for a shared cache since it'll be cleared by the ApplicationContext.((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache();}}

2.1 Parse1

从当前的Bean 定义文件集合中查找@Configuration修饰的类, 如果没有找到直接返回。

	for (String beanName : candidateNames) {BeanDefinition beanDef = registry.getBeanDefinition(beanName);if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {if (logger.isDebugEnabled()) {logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);}}else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));}}// Return immediately if no @Configuration classes were foundif (configCandidates.isEmpty()) {return;}

2.2 Parse2

对Configuration类进行排序。

		configCandidates.sort((bd1, bd2) -> {int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());return Integer.compare(i1, i2);});

2.3 Parse3

检查是否有配置的Bean 名称生成策略。

	    SingletonBeanRegistry sbr = null;if (registry instanceof SingletonBeanRegistry) {sbr = (SingletonBeanRegistry) registry;if (!this.localBeanNameGeneratorSet) {BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR);if (generator != null) {this.componentScanBeanNameGenerator = generator;this.importBeanNameGenerator = generator;}}}

2.4 Parse4

设置环境上下文。

		if (this.environment == null) {this.environment = new StandardEnvironment();}

2.5 Parse5

解析@Configuration配置类。

ConfigurationClassParser parser = new ConfigurationClassParser(this.metadataReaderFactory, this.problemReporter, this.environment,this.resourceLoader, this.componentScanBeanNameGenerator, registry);Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());do {parser.parse(candidates);parser.validate();Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());configClasses.removeAll(alreadyParsed);// Read the model and create bean definitions based on its contentif (this.reader == null) {this.reader = new ConfigurationClassBeanDefinitionReader(registry, this.sourceExtractor, this.resourceLoader, this.environment,this.importBeanNameGenerator, parser.getImportRegistry());}this.reader.loadBeanDefinitions(configClasses);alreadyParsed.addAll(configClasses);candidates.clear();if (registry.getBeanDefinitionCount() > candidateNames.length) {String[] newCandidateNames = registry.getBeanDefinitionNames();Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));Set<String> alreadyParsedClasses = new HashSet<>();for (ConfigurationClass configurationClass : alreadyParsed) {alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());}for (String candidateName : newCandidateNames) {if (!oldCandidateNames.contains(candidateName)) {BeanDefinition bd = registry.getBeanDefinition(candidateName);if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&!alreadyParsedClasses.contains(bd.getBeanClassName())) {candidates.add(new BeanDefinitionHolder(bd, candidateName));}}}candidateNames = newCandidateNames;}}while (!candidates.isEmpty());

1. 解析@Configuration, 根据配置扫描该路径下的@Configuration, @Controller, @Service, @Component等注解。
2. 通过ConfigurationClassBeanDefinitionReader添加到当前registry中。

3.ConfigurationClassParser解析

通过ConfigurationClassParser 解析每一个@Configuration标记的类

doProcessConfigurationClass:

	@Nullableprotected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)throws IOException {if (configClass.getMetadata().isAnnotated(Component.class.getName())) {// Recursively process any member (nested) classes firstprocessMemberClasses(configClass, sourceClass, filter);}// Process any @PropertySource annotationsfor (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(sourceClass.getMetadata(), PropertySources.class,org.springframework.context.annotation.PropertySource.class)) {if (this.propertySourceRegistry != null) {this.propertySourceRegistry.processPropertySource(propertySource);}else {logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +"]. Reason: Environment must implement ConfigurableEnvironment");}}// Process any @ComponentScan annotationsSet<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);if (!componentScans.isEmpty() &&!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {for (AnnotationAttributes componentScan : componentScans) {// The config class is annotated with @ComponentScan -> perform the scan immediatelySet<BeanDefinitionHolder> scannedBeanDefinitions =this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());// Check the set of scanned definitions for any further config classes and parse recursively if neededfor (BeanDefinitionHolder holder : scannedBeanDefinitions) {BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();if (bdCand == null) {bdCand = holder.getBeanDefinition();}if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {parse(bdCand.getBeanClassName(), holder.getBeanName());}}}}// Process any @Import annotationsprocessImports(configClass, sourceClass, getImports(sourceClass), filter, true);// Process any @ImportResource annotationsAnnotationAttributes importResource =AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);if (importResource != null) {String[] resources = importResource.getStringArray("locations");Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");for (String resource : resources) {String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);configClass.addImportedResource(resolvedResource, readerClass);}}// Process individual @Bean methodsSet<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);for (MethodMetadata methodMetadata : beanMethods) {configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));}// Process default methods on interfacesprocessInterfaces(configClass, sourceClass);// Process superclass, if anyif (sourceClass.getMetadata().hasSuperClass()) {String superclass = sourceClass.getMetadata().getSuperClassName();if (superclass != null && !superclass.startsWith("java") &&!this.knownSuperclasses.containsKey(superclass)) {this.knownSuperclasses.put(superclass, configClass);// Superclass found, return its annotation metadata and recursereturn sourceClass.getSuperClass();}}// No superclass -> processing is completereturn null;}

解析@Component, @PropertySources, @ComponentScans, @Import, @ImportResource, @Bean注解是否在此类上和其内部。

@ComponentScans为例: 这个parse#doParse(): 通过循环去检查是否符合, 然后封装为scannerBeanDefinition集合。通过遍历集合得到BeanDefinitionHolder中的beanDefinition, 然后解析其中的内容。

parse -> doScan方法, 通过ClassPathBeanDefinitionScanner扫描帮助解析类的内容。

4.ConfigurationClassBeanDefinitionReader解析

通过ConfigurationClassBeanDefinitionReader#loadBeanDefinitions()方法将上面通过ConfigurationClassParser解析得到的BeanDefinition集合读取和注册进register。

	private void loadBeanDefinitionsForConfigurationClass(ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {if (trackedConditionEvaluator.shouldSkip(configClass)) {String beanName = configClass.getBeanName();if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {this.registry.removeBeanDefinition(beanName);}this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName());return;}if (configClass.isImported()) {registerBeanDefinitionForImportedConfigurationClass(configClass);}for (BeanMethod beanMethod : configClass.getBeanMethods()) {loadBeanDefinitionsForBeanMethod(beanMethod);}loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());}

将一个ConfigurationClass和它内部所有被@Bean标记的方法, 变成BeanDefinition, 注册进register。

1. 如果当前类是通过@Import被别的配置类引入,则将当前类转化成bean definition注册.
2. 将当前类的所有被@Bean标记方法,转化为bean definition注册到当前registry
3. 解析当前类上@ImportResource
4. 解析当前类引入的ImportBeanDefinitionRegistrar接口的子类.

4.1@Bean方法解析成BeanDefinition

/*** Read the given {@link BeanMethod}, registering bean definitions* with the BeanDefinitionRegistry based on its contents.*/private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {ConfigurationClass configClass = beanMethod.getConfigurationClass();MethodMetadata metadata = beanMethod.getMetadata();String methodName = metadata.getMethodName();// Do we need to mark the bean as skipped by its condition?if (this.conditionEvaluator.shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN)) {configClass.skippedBeanMethods.add(methodName);return;}if (configClass.skippedBeanMethods.contains(methodName)) {return;}AnnotationAttributes bean = AnnotationConfigUtils.attributesFor(metadata, Bean.class);Assert.state(bean != null, "No @Bean annotation attributes");// Consider name and any aliasesList<String> names = new ArrayList<>(Arrays.asList(bean.getStringArray("name")));String beanName = (!names.isEmpty() ? names.remove(0) : methodName);// Register aliases even when overriddenfor (String alias : names) {this.registry.registerAlias(beanName, alias);}// Has this effectively been overridden before (e.g. via XML)?if (isOverriddenByExistingDefinition(beanMethod, beanName)) {if (beanName.equals(beanMethod.getConfigurationClass().getBeanName())) {throw new BeanDefinitionStoreException(beanMethod.getConfigurationClass().getResource().getDescription(),beanName, "Bean name derived from @Bean method '" + beanMethod.getMetadata().getMethodName() +"' clashes with bean name for containing configuration class; please make those names unique!");}return;}ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass, metadata);beanDef.setResource(configClass.getResource());beanDef.setSource(this.sourceExtractor.extractSource(metadata, configClass.getResource()));if (metadata.isStatic()) {// static @Bean methodbeanDef.setBeanClassName(configClass.getMetadata().getClassName());beanDef.setFactoryMethodName(methodName);}else {// instance @Bean methodbeanDef.setFactoryBeanName(configClass.getBeanName());beanDef.setUniqueFactoryMethodName(methodName);}beanDef.setAutowireMode(RootBeanDefinition.AUTOWIRE_CONSTRUCTOR);beanDef.setAttribute(RequiredAnnotationBeanPostProcessor.SKIP_REQUIRED_CHECK_ATTRIBUTE, Boolean.TRUE);AnnotationConfigUtils.processCommonDefinitionAnnotations(beanDef, metadata);Autowire autowire = bean.getEnum("autowire");if (autowire.isAutowire()) {beanDef.setAutowireMode(autowire.value());}String initMethodName = bean.getString("initMethod");if (StringUtils.hasText(initMethodName)) {beanDef.setInitMethodName(initMethodName);}String destroyMethodName = bean.getString("destroyMethod");beanDef.setDestroyMethodName(destroyMethodName);// Consider scopingScopedProxyMode proxyMode = ScopedProxyMode.NO;AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(metadata, Scope.class);if (attributes != null) {beanDef.setScope(attributes.getString("value"));proxyMode = attributes.getEnum("proxyMode");if (proxyMode == ScopedProxyMode.DEFAULT) {proxyMode = ScopedProxyMode.NO;}}// Replace the original bean definition with the target one, if necessaryBeanDefinition beanDefToRegister = beanDef;if (proxyMode != ScopedProxyMode.NO) {BeanDefinitionHolder proxyDef = ScopedProxyCreator.createScopedProxy(new BeanDefinitionHolder(beanDef, beanName), this.registry,proxyMode == ScopedProxyMode.TARGET_CLASS);beanDefToRegister = new ConfigurationClassBeanDefinition((RootBeanDefinition) proxyDef.getBeanDefinition(), configClass, metadata);}if (logger.isDebugEnabled()) {logger.debug(String.format("Registering bean definition for @Bean method %s.%s()",configClass.getMetadata().getClassName(), beanName));}this.registry.registerBeanDefinition(beanName, beanDefToRegister);}

该方法是生成一个ConfigurationClassBeanDefinition, 并将其注册到registry。

1. 设置Bean定义来源
2. 设置工厂名称/工厂方法
3. 设置Autowire方式
4. 设置initMethod/destoryMethod
5. 设置scope

一个@Configuration类的@Bean会作为一个工厂bean的方式添加到registry中, 实例化Bean时候, 会调用工厂对应的方法。

5.@Configuration总结

ConfigurationClassPostProcessor- > ConfigurationClassParser / ConfigurationClassPostProcessorReader -> 解析@Bean等注解。

1. 注册时机: AnnotationConfigApplicationContext#this#AnnotatedBeanDefinitionReader#this -> AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry)

2. 执行时机： AbstractApplicationContext#refresh()#invokeBeanFactoryPostProcessors(beanFactory)
   生成对应的BeanDefinition注册到当前BeanDefinitionRegistry中。

3. 解析内容
   1. @Bean方法
   2. @Import注解,引入的其他@Configuration类或ImportBeanDefinitionRegistrar子类
   3. @ImportResource注解

4. 当前@Configuration标记的类也会作为一个bean添加到BeanDefinitionRegistry