Spring IOC @Configuration注解分析
引入在使用SpringBoot开发时，最常用的注解有@Component、@Service、@Controller、@Configuration等。当类使用这些注解标记时，类会被Spring IOC容器管理，包括创建，填充属性和实例化。
但是Spring容器如何发现并将这些类放到容器进行管理呢？
今天这篇博客主要分析Spring如何处理@Configuration注解。
@Configuration定义
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {
@AliasFor(annotation = Component.class)
String value() default "";
//Since: 5.2
boolean proxyBeanMethods() default true;
//Since: 6.0
boolean enforceUniqueMethods() default true;
}看Configuration注解的定义，它本质也是一个@Component注解。
所以，标记有@Configuration注解的类在Spring注册bean的第一阶段就会被注册到容器中，但是使用@Configuration注解的类内部的其他bean并没有被注册到容器中。
想知道@Configuration注解被如何处理，需要看invokeBeanFactoryPostProcessors 方法。
ConfigurationClassPostProcessor处理@Configuration注解
先大致说一下invokeBeanFactoryPostProcessors 方法的基本流程，因为这个方法会处理所有BeanDefinitionRegistryPostProcessor和BeanFactoryPostProcessor接口的子类：
[*]先处理方法入参：beanFactoryPostProcessors（如果只是分析AnnotationConfigApplicationContext，这个参数是空的。只有在分析SpringBoot的启动过程时，这个参数才会有值）
[*]再处理BeanDefinitionRegistryPostProcessor的子类
[*]这里最重要的一件事情是调用ConfigurationClassPostProcessor的processConfigBeanDefinitions方法。
[*]最后处理BeanFactoryPostProcessor的子类
invokeBeanFactoryPostProcessors 的部分代码：
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
Set<String> processedBeans = new HashSet<>();
if (beanFactory instanceof BeanDefinitionRegistry) {
//省略部分代码，处理入参：beanFactoryPostProcessors
//开始处理BeanDefinitionRegistryPostProcessor接口的子类
//保存所有符合的子类，即实现BeanDefinitionRegistryPostProcessor，同样实现PriorityOrdered
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
//调用currentRegistryProcessors中所有的BDRPP
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
//省略部分代码，同样处理BeanDefinitionRegistryPostProcessor接口的子类
}
else {
//省略部分代码
}
//省略部分代码 处理BeanFactoryPostProcessor接口的子类
}以上是invokeBeanFactoryPostProcessors的部分代码，接下来看ConfigurationClassPostProcessor的processConfigBeanDefinitions方法，在这个方法里开始正式地处理@Configruation注解：
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
String[] candidateNames = registry.getBeanDefinitionNames();
//遍历所有的候选者
for (String beanName : candidateNames) {
BeanDefinition beanDef = registry.getBeanDefinition(beanName);
if (beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE) != null) {
if (logger.isDebugEnabled()) {
logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
}
}
//校验候选者类上是否使用了@Configuration注解
else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}
//如果configCandidates为空，则立即返回
if (configCandidates.isEmpty()) {
return;
}
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});
SingletonBeanRegistry sbr = null;
if (registry instanceof SingletonBeanRegistry) {
sbr = (SingletonBeanRegistry) registry;
if (!this.localBeanNameGeneratorSet) {
BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(
AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR);
if (generator != null) {
this.componentScanBeanNameGenerator = generator;
this.importBeanNameGenerator = generator;
}
}
}
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// 创建一个解析@Configuration的解析器
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 {
StartupStep processConfig = this.applicationStartup.start("spring.context.config-classes.parse");
//开始解析候选类
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 content
if (this.reader == null) {
this.reader = new ConfigurationClassBeanDefinitionReader(
registry, this.sourceExtractor, this.resourceLoader, this.environment,
this.importBeanNameGenerator, parser.getImportRegistry());
}
//注册解析后的类到容器中
this.reader.loadBeanDefinitions(configClasses);
alreadyParsed.addAll(configClasses);
processConfig.tag("classCount", () -> String.valueOf(configClasses.size())).end();
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 classes
if (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();
}
}这个方法的关键点：
[*]找到所有要解析的类
[*]创建一个解析者
[*]开始解析类
[*]记住，这里只是解析，也就是确认所有需要处理的类或者方法，这些类或者方法最终也会注册到容器中
[*]注册解析后的类到容器中：this.reader.loadBeanDefinitions(configClasses);
解析
那么实际上如何解析呢？
protected final SourceClass doProcessConfigurationClass(
ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)
throws IOException {
//1. 判断当前类是否有内部类，如果有内部类是否使用了@Configuration注解，如果使用了该注解，那么需要先处理内部类的配置
//存在这种可能，但是实际开发中很少使用
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
processMemberClasses(configClass, sourceClass, filter);
}
// 处理@PropertySource注解
for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), PropertySources.class,
org.springframework.context.annotation.PropertySource.class)) {
if (this.environment instanceof ConfigurableEnvironment) {
processPropertySource(propertySource);
}
else {
logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
"]. Reason: Environment must implement ConfigurableEnvironment");
}
}
// 处理@ComponentScan注解
Set<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) {
Set<BeanDefinitionHolder> scannedBeanDefinitions =
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
for (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());
}
}
}
}
// 处理@Import注解
processImports(configClass, sourceClass, getImports(sourceClass), filter, true);
// 处理@ImportResource注解
AnnotationAttributes 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);
}
}
// 处理使用了@Bean的方法
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// Process default methods on interfaces
processInterfaces(configClass, sourceClass);
// Process superclass, if any
if (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 recurse
return sourceClass.getSuperClass();
}
}
// No superclass -> processing is complete
return null;
}processImports方法主要处理两种情况：
[*]实现ImportSelector接口的类
[*]实现ImportBeanDefinitionRegistrar接口的类
但是需要注意，这个方法只是把这些类放到了集合中，但是还没有开始处理。
下面开始看如何处理使用@Bean的方法
@Configuration
@Import(MyBeanFactoryPostProcessor.class)
public class JavaConfig {
@Bean
public Country country() {
return new Country();
}
}最后返回所有需要处理的方法。
注册
public class MyBeanFactoryPostProcessor implements ImportBeanDefinitionRegistrar {
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry, BeanNameGenerator importBeanNameGenerator) {
ImportBeanDefinitionRegistrar.super.registerBeanDefinitions(importingClassMetadata, registry, importBeanNameGenerator);
RootBeanDefinition rootBeanDefinition = new RootBeanDefinition();
rootBeanDefinition.setBeanClass(Person.class);
registry.registerBeanDefinition("person", rootBeanDefinition);
}
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
ImportBeanDefinitionRegistrar.super.registerBeanDefinitions(importingClassMetadata, registry);
}
}
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