09、SpringBoot 启动 刷新应用上下文 自动装配解析(一)
目录：Springboot源码学习目录
上文：08、SpringBoot 启动 准备应用上下文
前言：
一、属性应用上下文
debug进入refreshContext方法
private void refreshContext(ConfigurableApplicationContext context) {
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
// 进入刷新方法
refresh((ApplicationContext) context);
}
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(ConfigurableApplicationContext.class, applicationContext);
// 进入重载刷新方法
refresh((ConfigurableApplicationContext) applicationContext);
}
protected void refresh(ConfigurableApplicationContext applicationContext) {
// 调用上下文自己的刷新方法
applicationContext.refresh();
}
调用到上下文自己的刷新方法，我们就发现就是之前的spring的逻辑
原有的spring逻辑我们就不再看了，这里只看一下springboot特有并且比较重要的的逻辑
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// beanFactory后处理，向工厂中注入WebApplicationContextServletContextAwareProcessor，这一步我们不用太关心
postProcessBeanFactory(beanFactory);
StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
// 回调所有的 BeanFactoryPostProcessor，其中自动装配就是在该步完成，重点要关心的
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
beanPostProcess.end();
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 创建并启动 Tomcat 服务器，就是在该步完成，重点要关心的
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
contextRefresh.end();
}
}
}
二、回调所有的 BeanFactoryPostProcessor
debug进入invokeBeanFactoryPostProcessors方法
protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
// 调用后置处理注册器工具类，将获取到到的 BeanFactoryPostProcessor 实例化并调用
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 (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
}
PostProcessorRegistrationDelegate的invokeBeanFactoryPostProcessors方法逻辑很复杂，这个和Spring一样，这里我们只看和自动装配有关的那个 BeanFactoryPostProcessor
public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// 省略不重要逻辑---
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);
// 在呈现的部分代码里上面那部分代码就是获取所有BeanDefinitionRegistryPostProcessor的实现类，然后调用
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
currentRegistryProcessors.clear();
// 省略不重要逻辑---
}
然后遍历所有的BeanDefinitionRegistryPostProcessor的实现类
我们在前文创建 应用上下文时说过，在创建过程中想上下文beanFactory中注册了一个ConfigurationClassPostProcessor，这个类也实现了BeanDefinitionRegistryPostProcessor
ConfigurationClassPostProcessor也是我们重点关注的类，自动装配就和他有关系，我们只需要debug他就可以了
private static void invokeBeanDefinitionRegistryPostProcessors(
Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {
for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process")
.tag("postProcessor", postProcessor::toString);
// 找到ConfigurationClassPostProcessor然后执行
postProcessor.postProcessBeanDefinitionRegistry(registry);
postProcessBeanDefRegistry.end();
}
}
进入ConfigurationClassPostProcessor
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
// 省略不重要代码 ......
// ConfigurationClassPostProcessor解析的核心方法
processConfigBeanDefinitions(registry);
}
然后我们进入ConfigurationClassPostProcessor的processConfigBeanDefinitions方法，
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
// 获取当前beanFactory中的所有beanName
String[] candidateNames = registry.getBeanDefinitionNames();
// 遍历当前beanFactory中的所有beanName，因为还出去回调beanFactroyPostProcessor阶段，工厂中的beanName只有几个
for (String beanName : candidateNames) {
// 获取beanName对应的BeanDefinition
BeanDefinition beanDef = registry.getBeanDefinition(beanName);
// CONFIGURATION_CLASS_ATTRIBUTE = "org.springframework.context.annotation.ConfigurationClassPostProcessor.configurationClass"
// 如果BeanDefinition 中有 CONFIGURATION_CLASS_ATTRIBUTE属性，说明这个bean已经被解析过了，不需要再解析
if (beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE) != null) {
if (logger.isDebugEnabled()) {
logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
}
}
// 如果BeanDefinition 中没有 CONFIGURATION_CLASS_ATTRIBUTE属性，则需要判断是否需要解析
// 判断逻辑就不看了，在这里直接写，当类上面标注了@Configuration/@Component/@ComponentScan/@Import/@ImportResource等注解，就是配置类，需要进行后面的解析
// 这个工具类的方法后面还会用到
else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
}
}
// Return immediately if no @Configuration classes were found
// 判断是否为空，如果为空则说明没有需要解析的配置类，直接返回，一般第一次启动，我们能拿到的配置类就是我们的启动类，
if (configCandidates.isEmpty()) {
return;
}
// Sort by previously determined @Order value, if applicable
// 对需要解析的配置类进行排序
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;
// registry实现了SingletonBeanRegistry，此处为true
if (registry instanceof SingletonBeanRegistry) {
// 将registry强转为SingletonBeanRegistry
sbr = (SingletonBeanRegistry) registry;
// 默认为false，此处也成立
if (!this.localBeanNameGeneratorSet) {
// 从工厂中获取org.springframework.context.annotation.internalConfigurationBeanNameGenerator，对应的bean
BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(
AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR);
// 第一次创建应用上下文，为空，
if (generator != null) {
this.componentScanBeanNameGenerator = generator;
this.importBeanNameGenerator = generator;
}
}
}
// 实例化时将上下文中的环境赋值给了当前对象，此处不为空
if (this.environment == null) {
this.environment = new StandardEnvironment();
}
// Parse each @Configuration class
// 配置类解析器，不要被此处的英文误导了，这个解析器可以解析@Component，@PropertySources，@ComponentScans，@Import，@ImportResource，@Bean这些注解
ConfigurationClassParser parser = new ConfigurationClassParser(
this.metadataReaderFactory, this.problemReporter, this.environment,
this.resourceLoader, this.componentScanBeanNameGenerator, registry);
// 将待解析的BeanDefinitionHolder存入candidates集合，后面遍历解析
Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
// 收集已经解析过的类
Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
// 循环解析
do {
StartupStep processConfig = this.applicationStartup.start("spring.context.config-classes.parse");
// 开始解析 上面存入candidates集合的配置类，核心逻辑
parser.parse(candidates);
// 遍历所有解析出来的类，检查标注有@Configuration注解且proxyBeanMethods属性=true的类与其@bean标注的方法是不是fianl关键字修饰，如果是则报错
parser.validate();
// 获取所有的解析出来的配置类，存入configClasses集合
Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
//删除掉配置类集合中已经解析过的配置类，防止重复解析
configClasses.removeAll(alreadyParsed);
// Read the model and create bean definitions based on its content
// 如果读取器为空，则创建一个，配置类bean定义信息读取器，该读取器专门将配置类解析成BeanDefinition
if (this.reader == null) {
this.reader = new ConfigurationClassBeanDefinitionReader(
registry, this.sourceExtractor, this.resourceLoader, this.environment,
this.importBeanNameGenerator, parser.getImportRegistry());
}
// 将配置类解析为beanDefinition，核心逻辑
this.reader.loadBeanDefinitions(configClasses);
// 将解析过的配置类加入已解析集合
alreadyParsed.addAll(configClasses);
processConfig.tag("classCount", () -> String.valueOf(configClasses.size())).end();
// 清空待解析的配置类
candidates.clear();
// 如果解析后的 BeanDefinition 的总数 > 大于解析前的 BeanDefinition 的总数，则需要检查新增的bean中是否有配置类
if (registry.getBeanDefinitionCount() > candidateNames.length) {
// 获取所有的beanName
String[] newCandidateNames = registry.getBeanDefinitionNames();
// 获取所有解析之前的beanName
Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));
// 收集所有已解析的beanName
Set<String> alreadyParsedClasses = new HashSet<>();
for (ConfigurationClass configurationClass : alreadyParsed) {
alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());
}
// 遍历所有的beanName,如果他在解析之前不存在，则获取他的他BeanDefinition
for (String candidateName : newCandidateNames) {
if (!oldCandidateNames.contains(candidateName)) {
BeanDefinition bd = registry.getBeanDefinition(candidateName);
// 然后检查，这个类是不是配置类，并且没有解析过，如果是，则加入待解析的配置类中
if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&
!alreadyParsedClasses.contains(bd.getBeanClassName())) {
candidates.add(new BeanDefinitionHolder(bd, candidateName));
}
}
}
/// 同时将解析前所有配置类更新
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();
}
}
上面这段解析流程中，最重要的是parser.parse(candidates);和this.reader.loadBeanDefinitions(configClasses);这两行代码
parser.parse(candidates);代表的是将待解析的配置类中的类解析出来，而自动装配的逻辑也在其中
this.reader.loadBeanDefinitions(configClasses);代表的时候将解析出来的类，转化为 BeanDefinition
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