Spring IOC - ConfigurationClassPostProcessor源码解析
上文提到Spring在Bean扫描过程中，会手动将5个Processor类注册到beanDefinitionMap中，其中ConfigurationClassPostProcessor就是本文将要讲解的内容，该类会在refresh()方法中通过调用invokeBeanFactoryPosstProcessors(beanFactory)被调用。
5个Processor类列表如下：
|
类名
|
是否BeanDefinitionRegistryPostProcessor
|
是否BeanFactoryPostProcessor
|
是否BeanPostProcessor
|
|
ConfigurationClassPostProcessor
|
是
|
是
|
是
|
|
AutowiredAnnotationBeanPostProcessor
|
否
|
否
|
是
|
|
CommonAnnotationBeanPostProcessor
|
否
|
否
|
是
|
|
EventListenerMethodProcessor
|
否
|
是
|
否
|
|
DefaultEventListenerFactory
|
否
|
否
|
否
|
ConfigurationClassPostProcessor中两个核心方法将被调用，其主要作用如下：
| 方法名 |
作用 |
| postProcessBeanDefinitionRegistry() |
（1）@Conditional注解条件解析 （2）被以下注解标注的类及内部类 @Component、@PropertySources、@PropertySource、@ComponentScans、@ComponentScan、@Import、@ImportResource、@Bean、接口中的@Bean |
| postProcessBeanFactory() |
对full模式的配置类BeanDefinition进行CGLib增强：把CGLib生成的子类型设置到beanDefinition中 |
postProcessBeanDefinitionRegistry()源码及注释如下：
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
int registryId = System.identityHashCode(registry);
if (this.registriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanDefinitionRegistry already called on this post-processor against " + registry);
}
if (this.factoriesPostProcessed.contains(registryId)) {
throw new IllegalStateException(
"postProcessBeanFactory already called on this post-processor against " + registry);
}
this.registriesPostProcessed.add(registryId);
// 执行解析和扫描
processConfigBeanDefinitions(registry);
}
进入processConfigBeanDefinitions(registry)方法，其主体逻辑流程图如下：
其中标红步骤为两个关键步骤：
1. 通过beanDefinition判断是否为配置类
Spring专门提供了一个工具类：ConfigurationClassUtils来检查是否为配置类，并标记full、lite模式，逻辑如下：
2. 解析配置类
doProcessConfigurationClass即为真正的对个注解的解析方法，其逻辑流程图如下：
具体的源码及详细注释如下：
1. 主流程processConfigBeanDefinitions方法：
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
// 候选配置类定义列表
List configCandidates = new ArrayList<>();
// 获取容器中所有bean定义的名字
String[] candidateNames = registry.getBeanDefinitionNames();
for (String beanName : candidateNames) {
// 获取bean定义
BeanDefinition beanDef = registry.getBeanDefinition(beanName);
// org.springframework.context.annotation.ConfigurationClassPostProcessor.configurationClass
// Bean Definition是否已经被标记为配置类(full、lite模式)
if (beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE) != null) {
if (logger.isDebugEnabled()) {
logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
}
}
// 查看bean是否是ConfigurationClass
//被@Configuration、@Component、@ComponentScan、@Import、@ImportResource、@Bean标记
else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
// 是配置类，则加入到候选列表
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}
// Return immediately if no @Configuration classes were found
// 如果为空，即找不到被@Configuration、@Component、@ComponentScan、@Import、@ImportResource、@Bean标记的类，则立即返回
if (configCandidates.isEmpty()) {
return;
}
// Sort by previously determined @Order value, if applicable
// 对需要处理的BeanDefinition排序，值越小越靠前
configCandidates.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 context
// 检查是否有自定义的beanName生成器
SingletonBeanRegistry sbr = null;
if (registry instanceof SingletonBeanRegistry) {
sbr = (SingletonBeanRegistry) registry;
if (!this.localBeanNameGeneratorSet) {
//获取自定义的beanName生成器
BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(
AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR);
if (generator != null) {
// 如果spring有自定义的beanName生成器，则重新赋值
this.componentScanBeanNameGenerator = generator;
this.importBeanNameGenerator = generator;
}
}
}
//如果环境对象为空，则创建新的环境对象
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// 构造一个配置类解析器，用来把bean定义的重要信息提取转化为ConfigurationClass
// Parse each @Configuration class
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
// 候选配置类定义列表（查重）
Set candidates = new LinkedHashSet<>(configCandidates);
// 存储已解析的配置类列表
Set alreadyParsed = new HashSet<>(configCandidates.size());
do {
// 解析配置类
parser.parse(candidates);
// 配置类不能被申明为final(因为CGLIB的限制)，除非它声明proxyBeanMethods=false
// 在@Configuration类中，@Bean方法的实例必须是可重写的，以适应CGLIB
parser.validate();
// 获取解析器中解析出的配置类ConfigurationClass: parser.getConfigurationClasses()
Set configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
// 过滤掉已解析的配置类
configClasses.removeAll(alreadyParsed);
// 构造一个bean定义读取器
// 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());
}
// 读取ConfigurationClass获取衍生bean定义并注册到容器
// 核心方法，将完全填充好的ConfigurationClass实例转化为BeanDefinition注册入IOC容器
this.reader.loadBeanDefinitions(configClasses);
// 加入已解析配置类
alreadyParsed.addAll(configClasses);
// 清空候选配置类定义列表
candidates.clear();
// 如果容器中bean定义有新增
if (registry.getBeanDefinitionCount() > candidateNames.length) {
// 查找出新增的配置类bean定义 start
String[] newCandidateNames = registry.getBeanDefinitionNames();
Set oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));
Set 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
// 如果想要在@Configuration类中使用ImportAware接口，需要将ImportRegistry注册为bean。这样，@Configuration类就可以
// 使用ImportRegistry来获取导入的类信息
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.
// 如果MetadataReaderFactory是由外部提供的，则需要清楚其缓存。但是，如果MetadataReaderFactory是由ApplicationContext共享的，则不需要进行清除，
// 因为ApplicationContext会自动清楚共享缓存
((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache();
}
} 2. 其中检查是否为配置类方法ConfigurationClassUtils.checkConfigurationClassCandidate
//检查给定的BeanDefinition是否是一个配置类的候选者(或一个在配置/组件类中声明的嵌套组件类)
//并对其进行相应的标记处理
//被@Configuration、@Component、@ComponentScan、@Import、@ImportResource、@Bean标记
public static boolean checkConfigurationClassCandidate(
BeanDefinition beanDef, MetadataReaderFactory metadataReaderFactory) {
//获取bean定义信息中的class类名
String className = beanDef.getBeanClassName();
//如果className为空，或者bean定义信息中的factoryMethod不等于空，那么直接返回
if (className == null || beanDef.getFactoryMethodName() != null) {
return false;
}
AnnotationMetadata metadata;
//通过注解注入的BeanDefinition都是AnnotatedGenericBeanDefinition，实现了AnnotatedBeanDefinition
//Spring内部的BeanDefinition都是RootBeanDefiniton，实现了AbstractBeanDefinition
//此处主要用于判断是否是归属于AnnotatedBeanDefinition
if (beanDef instanceof AnnotatedBeanDefinition &&
className.equals(((AnnotatedBeanDefinition) beanDef).getMetadata().getClassName())) {
// Can reuse the pre-parsed metadata from the given BeanDefinition...
// 从当前bean的定义信息中获取元素
metadata = ((AnnotatedBeanDefinition) beanDef).getMetadata();
}
//判断是否是Spring中默认的BeanDefinition
else if (beanDef instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) beanDef).hasBeanClass()) {
// Check already loaded Class if present...
// since we possibly can't even load the class file for this Class.
//获取当前bean对象的Class对象
Class beanClass = ((AbstractBeanDefinition) beanDef).getBeanClass();
//如果class实例是下面4种类或者接口的子类，父接口等任何一种情况，直接返回
if (BeanFactoryPostProcessor.class.isAssignableFrom(beanClass) ||
BeanPostProcessor.class.isAssignableFrom(beanClass) ||
AopInfrastructureBean.class.isAssignableFrom(beanClass) ||
EventListenerFactory.class.isAssignableFrom(beanClass)) {
return false;
}
//为给定类创建新的AnnotationMetadata
metadata = AnnotationMetadata.introspect(beanClass);
}
//如果上述两种情况都不符合
else {
try {
//获取className的MetadataReader实例
MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(className);
//读取底层类的完整注解元数据，包括带注解方法的元数据
metadata = metadataReader.getAnnotationMetadata();
}
catch (IOException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Could not find class file for introspecting configuration annotations: " +
className, ex);
}
return false;
}
}
// 获取Bean Definition的元数据被@Configuration注解标注的属性字典值
Map config = metadata.getAnnotationAttributes(Configuration.class.getName());
// 如果bean被@Configuration注解标注，并且proxyBeanMethods属性的值为true,则标注当前配置类为full，即需要代理增强，为一个代理类
if (config != null && !Boolean.FALSE.equals(config.get("proxyBeanMethods"))) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
}
// 如果存在，或者isConfigurationCandidate返回true,则标注当前配置类为lite,即不需要代理增强，为一个普通类
// 标注了Configuration注解且proxyBeanMethods属性的值为false，则为lite模式
// 没有标注Configuration注解，但是标注了Component、ComponentScan、Import、ImportResource、@Bean注解、则为lite模式
else if (config != null || isConfigurationCandidate(metadata)) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
}
// 组件类不存在@Configuration注解，直接返回false
else {
return false;
}
// 获取配置类的排序顺序，设置到组件定义属性中
// It's a full or lite configuration candidate... Let's determine the order value, if any.
//Bean Definition是一个标记为full/lite的候选项，如果有order属性就设置order属性
Integer order = getOrder(metadata);
if (order != null) {
//设置bean的order值
beanDef.setAttribute(ORDER_ATTRIBUTE, order);
}
return true;
} 3. 真正干活的方法doProessConfigurationClass
// 通过读取源类的注释、成员和方法来构建完整的ConfigurationClass
// 1.处理@Component
// 2.处理每个@PropertySource
// 3.处理每个@ComponentScan
// 4.处理每个Impoit
// 5.处理每个@ImportResource
// 6.找配置类中@Bean注解的方法(找出Class中存在@Bean标注的方法，加入到ConfigurationClass的beanMethods属性)
// 7.找接口中@Bean注解的方法
// 8.存在父类则递归处理
@Nullable
protected final SourceClass doProcessConfigurationClass(
ConfigurationClass configClass, SourceClass sourceClass, Predicate filter)
throws IOException {
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
// 递归处理嵌套的成员类
processMemberClasses(configClass, sourceClass, filter);
}
// Process any @PropertySource annotations
// 处理@PropertySources和@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");
}
}
// Process any @ComponentScan annotations
// 处理@ComponentScans和@ComponentScan注解
Set 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 immediately
// 配置类使用了注解@ComponentScan -> 立即执行扫描。
Set scannedBeanDefinitions =
this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
// Check the set of scanned definitions for any further config classes and parse recursively if needed
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());
}
}
}
}
// Process any @Import annotations
// 处理@Import注解
// getImports:递归获取@Import导入的类
processImports(configClass, sourceClass, getImports(sourceClass), filter, true);
// Process any @ImportResource annotations
// 处理@ImportResource注解
// 读取locations, reader属性，封装存放在importResources map集合中
AnnotationAttributes importResource =
AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
if (importResource != null) {
String[] resources = importResource.getStringArray("locations");
Class readerClass = importResource.getClass("reader");
for (String resource : resources) {
String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
configClass.addImportedResource(resolvedResource, readerClass);
}
}
// Process individual @Bean methods
// 处理@Bean方法
Set beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// Process default methods on interfaces
// 处理接口的默认方法实现，从jdk8开始，接口中的方法可以有自己的默认实现，因此如果这个接口的方法加了@Bean注解，也需要被解析
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;
}