SpringBoot配置类解析流程--整体流程
在之前的文章（SpringBoot的自动装配_lhf2112的博客-CSDN博客）中我们提到了SpringBoot配置类解析的核心类：ConfigurationClassPostProcessor这个类，以及其中的核心方法postProcessBeanDefinitionRegistry方法。ConfigurationClassPostProcessor是一个关键的后置处理器，它的主要作用是：能够解析和处理配置类中的注解和配置信息，包括@Bean方法的注册，@Import注解的处理，条件注解的判断和依赖注入的解析。由于流程比较复杂，因此还是单独拿一篇博文来学习一下比较好。
配置类解析的触发
我们还是再来补充下配置类解析在项目启动过程中的触发点吧。
SpringBoot项目启动的refresh方法中有一个invokeBeanFactoryPostProcessors方法：
/**
* Instantiate and invoke all registered BeanFactoryPostProcessor beans,
* respecting explicit order if given.
* Must be called before singleton instantiation.
*/
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
方法里面第一行的
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
会获得所有的BeanDefinitionRegistryPostProcessor的实现，进而调用它们的postProcessBeanDefinitionRegistry方法，而我们所关注的ConfigurationClassPostProcessor，就是其中之一。
配置类解析的流程
ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry
首先我们找到ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry方法
/**
* Derive further bean definitions from the configuration classes in the registry.
*/
@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);
processConfigBeanDefinitions(registry);
}此方法首先会获得Registry的一个唯一id，这个地方的Registry实际上就是org.springframework.beans.factory.support.DefaultListableBeanFactory；接下来看这个id是否在registriesPostProcessed或者factoriesPostProcessed中，如果在的话，就说明处理过了；否则，会将它加入registriesPostProcessed集合当中，然后调用processConfigBeanDefinitions方法；
ConfigurationClassPostProcessor#processConfigBeanDefinitions
这是个相当长的方法，这里还是贴上了整个方法以便于有一个整体上的思路：
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List 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 found
if (configCandidates.isEmpty()) {
return;
}
// Sort by previously determined @Order value, if applicable
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
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;
}
}
}
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// Parse each @Configuration class
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
Set candidates = new LinkedHashSet<>(configCandidates);
Set alreadyParsed = new HashSet<>(configCandidates.size());
do {
parser.parse(candidates);
parser.validate();
Set 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 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
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();
}
} 方法首先会从Registry获取所有的BeanDefinitionNames，BeanDefinition即Java类在Spring项目中的描述；接下来遍历BeanDefinitionNames，ConfigurationClassUtils.isFullConfigurationClass方法会获得CONFIGURATION_CLASS的属性，看这个属性是不是FULL，是FULL则说明被处理过，否则，再调用ConfigurationClassUtils.isLiteConfigurationClass得CONFIGURATION_CLASS的属性，看这个属性是不是LITE，如果是的话也说明被处理过了，这部分我们可以跳过，因为是没有被处理过的；
ConfigurationClassUtils#checkConfigurationClassCandidate
接下来走到ConfigurationClassUtils.checkConfigurationClassCandidate方法；这个方法还是有一些内容的，我们把代码贴到这里
/**
* Check whether the given bean definition is a candidate for a configuration class
* (or a nested component class declared within a configuration/component class,
* to be auto-registered as well), and mark it accordingly.
* @param beanDef the bean definition to check
* @param metadataReaderFactory the current factory in use by the caller
* @return whether the candidate qualifies as (any kind of) configuration class
*/
public static boolean checkConfigurationClassCandidate(
BeanDefinition beanDef, MetadataReaderFactory metadataReaderFactory) {
String className = beanDef.getBeanClassName();
if (className == null || beanDef.getFactoryMethodName() != null) {
return false;
}
AnnotationMetadata metadata;
if (beanDef instanceof AnnotatedBeanDefinition &&
className.equals(((AnnotatedBeanDefinition) beanDef).getMetadata().getClassName())) {
// Can reuse the pre-parsed metadata from the given BeanDefinition...
metadata = ((AnnotatedBeanDefinition) beanDef).getMetadata();
}
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.
Class beanClass = ((AbstractBeanDefinition) beanDef).getBeanClass();
metadata = new StandardAnnotationMetadata(beanClass, true);
}
else {
try {
MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(className);
metadata = metadataReader.getAnnotationMetadata();
}
catch (IOException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Could not find class file for introspecting configuration annotations: " +
className, ex);
}
return false;
}
}
if (isFullConfigurationCandidate(metadata)) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
}
else if (isLiteConfigurationCandidate(metadata)) {
beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
}
else {
return false;
}
// It's a full or lite configuration candidate... Let's determine the order value, if any.
Integer order = getOrder(metadata);
if (order != null) {
beanDef.setAttribute(ORDER_ATTRIBUTE, order);
}
return true;
}方法会首先进行空/空方法校验，接下来根据是AnnotatedBeanDefinition还是AbstractBeanDefinition来获取相应的元数据，由于注解方式是目前的主流，所以一般会调用AnnotatedBeanDefinition的方法；
接下来，我们再次判断CONFIGURATION_CLASS的属性，看这个属性是不是FULL，是不是LITE，如果是，会在beanDef设置好相关的属性；如果是@Configuration所注解的bean，会赋值为FULL，如果是类似@Component注解的bean，则会赋值为LITE；
回到processConfigBeanDefinitions我们来看下后续内容
如果没有 @Configuratio 注解的bean，会直接返回；接下来会按照@Order注解的值进行升序排序；
// Return immediately if no @Configuration classes were found
if (configCandidates.isEmpty()) {
return;
}
// Sort by previously determined @Order value, if applicable
configCandidates.sort((bd1, bd2) -> {
int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
return Integer.compare(i1, i2);
});在接下来会判断这个registry是不是SingletonBeanRegistry，DefaultListableBeanFactory是一个SingletonBeanRegistry，所以会进入if分支
// Detect any custom bean name generation strategy supplied through the enclosing application context
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;
}
}
}通常这里的BeanNameGenerator generator是为null的；
接下来判断environment是否为空，此处因为构建过了，所以是不为空的；
if (this.environment == null) {
this.environment = new StandardEnvironment();
}再接下来会构建一个ConfigurationClassParser，ConfigurationClassParser是一个配置类的解析工具；同时还会构建两个集合candidates以及alreadyParsed；
// Parse each @Configuration class
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
Set candidates = new LinkedHashSet<>(configCandidates);
Set alreadyParsed = new HashSet<>(configCandidates.size()); 顾名思义，candidates就是候选配置类集合，alreadyParsed就是解析过的配置类集合；
接下来 我们进入一个循环
do {
parser.parse(candidates);
parser.validate();
Set 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 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()); 这个就是配置类的解析流程了。配置类的解析流程是一个do-while循环，里面内容很多，足够另外一篇博文来进行分析，争取后续会更新相关的内容。
当candidates为空时，我们跳出循环，接下来会判断sbr(SingletonBeanRegistry)是否有importRegistry的bean，如果没有，就注册一个；然后判断metadataReaderFactory是不是CachingMetadataReaderFactory，如果是，则清空缓存；
// 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();
}到这里postProcessBeanDefinitionRegistry的整体流程就结束了，希望可以尽快地一起学习关于配置类的解析流程，do-while循环的详细分析。