接着上一篇 invokeBeanFactoryPostProcessors 来分析，主要分析 ConfigurationClassPostProcessor 作用。
前言
ConfigurationClassPostProcessor 对已经注册的 BeanDefinition 进行分析，如果有配置 @ComponentScan 等，则进一步扫描
添加
在初始化 AnnotationConfigApplicationContext 时候，会网beanDefs中加入一些默认配置bean：
org.springframework.context.annotation.internalConfigurationAnnotationProcessor：对应ConfigurationClassPostProcessororg.springframework.context.annotation.internalAutowiredAnnotationProcessor对应AutowiredAnnotationBeanPostProcessororg.springframework.context.annotation.internalCommonAnnotationProcessor"对应CommonAnnotationBeanPostProcessororg.springframework.context.annotation.internalPersistenceAnnotationProcessor对应org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessororg.springframework.context.event.internalEventListenerProcessor对应EventListenerMethodProcessororg.springframework.context.event.internalEventListenerFactory对应DefaultEventListenerFactory
上面有 和 @Autowired 、 @Configuration 以及其他一些通用注解相关的。
后面文章会一一分析。
ConfigurationClassPostProcessor 结构
先看看 ConfigurationClassPostProcessor 类结构：
public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {
...
}
从上面类定义，可以有以下几点：
- 实现了
PriorityOrdered优先级接口 - 实现了
ResourceLoaderAware，当初始化ConfigurationClassPostProcessor，会设置其内部的resourceLoaderAware - 实现
BeanClassLoaderAware， 会设置ClassLoader。 - 实现
EnvironmentAware，会设置Environment - 实现
BeanDefinitionRegistryPostProcessor接口，用于更改BeanDefinition。
调用
从上篇文章可知，在 invokeBeanFactoryPostProcessors 中被调用。具体调用路径：
applicationContext.refresh() -> invokeBeanFactoryPostProcessors(beanFactory) -> PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors()) -> invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry) -> postProcessor.postProcessBeanDefinitionRegistry(registry)
下面从 postProcessor.postProcessBeanDefinitionRegistry(registry) 中开始分析：
postProcessBeanDefinitionRegistry
先看代码：
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
// 设置registryId
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);
// 开始处理
processConfigBeanDefinitions(registry);
}
上面代码主要是设置 registryId，而主要处理在 processConfigBeanDefinitions，主要为解析 配置类 (configuration classes)
processConfigBeanDefinitions
该方法主要为验证即构建所有的 @Configuration 类：
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
String[] candidateNames = registry.getBeanDefinitionNames();
// 从所有的 BeanDefinition中获取配置类。
for (String beanName : candidateNames) {
BeanDefinition beanDef = registry.getBeanDefinition(beanName);
// 判断一个类是否为 @Configuration类并且已经处理过。
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)) {
// 如果是配置类，则加入
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}
// 如果啥也没找到，直接退出
if (configCandidates.isEmpty()) {
return;
}
// 根据 @Order 排序
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});
// 判断是否需要配置 BeanNameGenerator
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;
}
}
}
// 设置 environment
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// 解析每一个 @Configuration注解类
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 {
// 解析，具体步骤看下面第一小点
parser.parse(candidates);
// 验证
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());
}
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 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();
}
}
- FullConfiguration 候选指的是直接使用
@Configuration修饰 - LiteConfigurationCandidate 候选是指是否有``@Component
、@Bean、@Import`注解， processConfigBeanDefinitions这个方法是一个可递归的方法，即如果在 找到配置类中，有新的 类（例如@ComponentScan），则需要再一步解析下面的类。
parser.parse(candidates)
在此之前 所有已经注册的BeanDefinition 将在这里进一步解析，判断不同类型后，将每个BeanDefinitionHolder 放入 ConfigurationClassParser 的 parse 方法解析，而后进入 processConfigurationClass 方法：
protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
// 判断是否跳过该 bean的解析，通过 @Conditional 注解判断。
if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
return;
}
// 看是否已经解析过
ConfigurationClass existingClass = this.configurationClasses.get(configClass);
if (existingClass != null) {
if (configClass.isImported()) {
if (existingClass.isImported()) {
existingClass.mergeImportedBy(configClass);
}
// Otherwise ignore new imported config class; existing non-imported class overrides it.
return;
}
else {
// Explicit bean definition found, probably replacing an import.
// Let's remove the old one and go with the new one.
this.configurationClasses.remove(configClass);
this.knownSuperclasses.values().removeIf(configClass::equals);
}
}
// 获取一个 SourceClass
SourceClass sourceClass = asSourceClass(configClass);
do {
// 递归的去解析配置类 以及 它的 父类.
sourceClass = doProcessConfigurationClass(configClass, sourceClass);
}
while (sourceClass != null);
this.configurationClasses.put(configClass, configClass);
}
以上代码有以下几段逻辑：
- 判断是否要跳过该bean的加载解析，通过
@Conditional判定。 - 构造
SourceClass循环调用doProcessConfigurationClass进行解析。 - 在 doProcessConfigurationClass 则主要是解析具体过程。
doProcessConfigurationClass
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
throws IOException {
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// 如果该类，使用@Component注解，则递归搜寻内部类
processMemberClasses(configClass, sourceClass);
}
// 解析 @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");
}
}
// 解析 @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) {
// The config class is annotated with @ComponentScan -> perform the scan immediately
Set<BeanDefinitionHolder> 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());
}
}
}
}
// getImports 解析 @Import注解 ，进去会递归的扫描，即 @Import上的@Import 引入
processImports(configClass, sourceClass, getImports(sourceClass), true);
// 解析 @ImportResource
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);
}
}
// 解析独立的 @Bean注解
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// 解析 接口默认方法。Process default methods on interfaces
processInterfaces(configClass, sourceClass);
// 解析父类
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();
}
}
// 没有父类处理，所以只解析本类，那么返回null退出。
return null;
}
- 上面方法依次会解析
@Component、@PropertySource、@ComponentScans、@ImportResource、@Bean和 默认接口方法（这类也会以@Bean 注解方法处理。）。注解 - 如果该类，使用@Component注解，则递归向上 搜寻内部类
- 在 解析 @Import 注解时，会首先通过
getImports(sourceClass)向上获取所有的 @Import 中的value，而后，去到processImports方法中，将对应Import标签加入进来。 - 循环对所有的 FullConfigurationCandidate 和 LiteConfigurationCandidate的候选
BeanDefinition进行处理。
整个 ConfigurationClassPostProcessor 就分析完成，它是在 bean初始化之前，去解析配置类，将他们都加入到 Spring 的BeanDefinition 容器中，但此时尚未初始化。
觉得博主写的有用，不妨关注博主公众号: 六点A君。
哈哈哈，一起研究Spring：
