说明：源码基于Spring-5.2.2.RELEASE版本
ConfigurationClassPostProcessor 功能概述
ConfigurationClassPostProcessor 是spring框架中提供解析配置类的一个比较重要的后置处理器，其作用是解析被@Configuration注解的类，这个注解是一个类能被该后置处理器解析的必要条件；如果这些类还有如下这些注解，也会被依次解析：
- @Component
- @PropertySources
- @ComponentScan、@ComponentScans注解的类
- @Import注解的类
- @ImportResource
- @Bean注解的方法
- 其实现了BeanDefinitionRegistryPostProcessor和BeanFactoryPostProcessor：
在容器BeanFactory创建好并加载了优先级最高的beanDefinition后（正常流程来说，配置文件里配置的bean优先级最高），会执行 postProcessBeanDefinitionRegistry 方法(先)和 postProcessBeanFactory 方法(后）；
ConfigurationClassPostProcessor#processConfigBeanDefinitions
- postProcessBeanDefinitionRegistry 方法里解析BeanDefinition逻辑主要是processConfigBeanDefinitions方法完成的
方法签名：org.springframework.context.annotation.ConfigurationClassPostProcessor#processConfigBeanDefinitions
下面方法只保留了核心方法
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
String[] candidateNames = registry.getBeanDefinitionNames();
... 省略部分代码...
// 初始化解析器
// Parse each @Configuration class
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 {
//@A
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());
}
//@B
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());
... 省略部分代码...
}
@A：其主要逻辑是委托ConfigurationClassParser类来完成@Configuration类解析
@B：将ConfigurationClassParser扩展扫描到的类（注意这里是发现的所有类），类注册到beandefinition
ConfigurationClassParser#parse
以下是配置类【Configuration标记的类】流程控制核心方法：
org.springframework.context.annotation.ConfigurationClassParser#parse(java.util.Set<org.springframework.beans.factory.config.BeanDefinitionHolder>)
parse 方法不会进行beandefiniton的注册，只是通过扫描将beandefinition存入自己的configurationClasses属性，真正注册是在上面的@B处方法；
public void parse(Set<BeanDefinitionHolder> configCandidates) {
for (BeanDefinitionHolder holder : configCandidates) {
BeanDefinition bd = holder.getBeanDefinition();
try {
if (bd instanceof AnnotatedBeanDefinition) {
//@A
parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
}
else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
//@B
parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
}
else {
//@C
parse(bd.getBeanClassName(), holder.getBeanName());
}
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(
"Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);
}
}
//@D
this.deferredImportSelectorHandler.process();
}
//@A、@B、@C：调用parse方法解析配置配类
//@D：延时处理被@Import引入的DeferredImportSelector接口的子类。在@A、@B、@C方法中只会缓存被@Import引入的 DeferredImportSelector子类，不会做具体解析；spring boot中的AutoConfigurationImportSelector就是一个DeferredImportSelector子类；
DeferredImportSelector 的设计目的是在所有其他的配置类被处理后才处理。
上面parse 方法会调用 processConfigurationClass 方法
protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
return;
}
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);
}
}
// Recursively process the configuration class and its superclass hierarchy.
SourceClass sourceClass = asSourceClass(configClass);
do {
// @A
sourceClass = doProcessConfigurationClass(configClass, sourceClass);
}
while (sourceClass != null);
// @B
this.configurationClasses.put(configClass, configClass);
}
@A：doProcessConfigurationClass主要是解析配置类，如果配置类还有父类（不是以java开头的包）则返回值sourceClass就不会为空，则继续循环直到没有父类可以解析；
@B：将扫描到的bean存入configurationClasses属性
ConfigurationClassParser#doProcessConfigurationClass
1、该方法主要解析配置类里的 @Component，@PropertySources，@ComponentScans, @ComponentScan，@Import，@ImportResource 注解的类 和 @Bean 注解的 method；
2、其中如果被@ComponentScans, @ComponentScan扫描到有被@Configuration注解的类，则调用parse方法形成递归；
方法内容简要注释如下：
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
throws IOException {
// 1、如果该类有@Component注解，则解析内部嵌套的类（如果有）
if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
// Recursively process any member (nested) classes first
processMemberClasses(configClass, sourceClass);
}
// 2、如果目标类有@PropertySource注解，则解析其对应的字段
// Process any @PropertySource annotations
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");
}
}
// 3、解析@ComponentScans和@ComponentScan注解；扫描到待解析的目标类后，调用 parse方法对目标类进行进一步解析，调用parser方法会将目标类放入 configurationClasses 属性
// Process any @ComponentScan annotations
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)) {
// 调用 parse 方法，形成递归
parse(bdCand.getBeanClassName(), holder.getBeanName());
}
}
}
}
// 4、处理@Import注解，下面单独分析该方法
// Process any @Import annotations
processImports(configClass, sourceClass, getImports(sourceClass), true);
// 5、处理@ImportResource注解，下面单独分析该方法
// Process any @ImportResource annotations
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);
}
}
// 6、解析@Bean注解的方法
// Process individual @Bean methods
Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}
// Process default methods on interfaces
processInterfaces(configClass, sourceClass);
// 7、如果有父类，则返回父类信息，调用方判断返回值不是空会继续解析父类
// 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;
}
ConfigurationClassParser#processImports
该方法处理 @Import注解
private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass, Collection<SourceClass> importCandidates, boolean checkForCircularImports) {
if (importCandidates.isEmpty()) {
return;
}
//1、 检测报告循环依赖
if (checkForCircularImports && isChainedImportOnStack(configClass)) {
this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
} else {
this.importStack.push(configClass);
try {
for (SourceClass candidate : importCandidates) {
//2、 如果被Import的是ImportSelector实现类，
if (candidate.isAssignable(ImportSelector.class)) {
// Candidate class is an ImportSelector -> delegate to it to determine imports
Class<?> candidateClass = candidate.loadClass();
ImportSelector selector = ParserStrategyUtils.instantiateClass(candidateClass, ImportSelector.class,
this.environment, this.resourceLoader, this.registry);
//2.1、 如果是DeferredImportSelector的子类，则会被放入到 deferredImportSelectors 这个集合中待延迟处理；springboot的AutoConfigurationImportSelector.class就是这样的一种类
if (selector instanceof DeferredImportSelector) {
this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
}
else {
//2.2、 否则递归调用 processImports 方法，继续解析被@Import到的类 importSourceClasses
String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames);
processImports(configClass, currentSourceClass, importSourceClasses, false);
}
}
//3、 如果被引入的类是 ImportBeanDefinitionRegistrar子类，则会缓存到configClass对象的importBeanDefinitionRegistrars属性中
else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
// Candidate class is an ImportBeanDefinitionRegistrar ->
// delegate to it to register additional bean definitions
Class<?> candidateClass = candidate.loadClass();
ImportBeanDefinitionRegistrar registrar =
ParserStrategyUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class,
this.environment, this.resourceLoader, this.registry);
configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
}
//4、其他场景，比如直接@Import的一个类或者是通过2.2分支递归进入该方法，则调用processConfigurationClass方法形成递归，将解析到的类缓存进configurationClasses属性中
else {
// Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar ->
// process it as an @Configuration class
this.importStack.registerImport(
currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
processConfigurationClass(candidate.asConfigClass(configClass));
}
}
}
catch (BeanDefinitionStoreException ex) {
throw ex;
}
catch (Throwable ex) {
throw new BeanDefinitionStoreException(
"Failed to process import candidates for configuration class [" +
configClass.getMetadata().getClassName() + "]", ex);
}
finally {
this.importStack.pop();
}
}
}
- todo 20211118