1. Foreword knowledge
- Spring will scan all the classes managed by Spring, scan their class files, and parse them into BeanDefinition, which will describe the information of the class, for example: whether this class is a singleton, the type of Bean, whether it is lazy loading, Depends on which classes, autowired models. When Spring creates an object, it creates a Bean based on the information in the BeanDefinition.
- The Spring container in this article can be simply understood as DefaultListableBeanFactory, which is the implementation class of BeanFactory. This class has several very important attributes:
- beanDefinitionMap is a map used to store the BeanDefinition corresponding to the bean;
- beanDefinitionNames is a List collection used to store the names of all beans;
- singletonObjects is a Map used to store all created singleton beans.
- There are many post-processors in Spring, but they can be divided into two types in the end, one is BeanFactoryPostProcessor and the other is BeanPostProcessor. The former is used to intervene in the BeanFactory creation process, and the latter is used to intervene in the Bean creation process. The role of the post-processor is very important. The creation of beans and the realization of AOP all depend on the post-processor.
2. Source code analysis
2.1 Annotation-based
Process overview
This article is based on java-config technology analysis source code, so the entry here is AnnotationConfigApplicationContext, if you use xml analysis, then the entry is ClassPathXmlApplicationContext, the common feature of both of them is that they both inherit the AbstractApplicationContext class, and the famous refresh() is defined in this class. We then analyze the AnnotationConfigApplicationContext class, the entry is as follows:
AnnotationConfigApplicationContext applicationContext =
new AnnotationConfigApplicationContext(Config.class);
// 初始化容器
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
this();
// 注册配置类 BeanDefinition 到容器
register(annotatedClasses);
// 加载或者刷新容器中的Bean
refresh();
}
The startup process of the entire Spring container can be drawn as the following flow chart:
When the spring container is initialized, the no-argument constructor is called through this(), and the following three things are mainly done:
(1) Instantiate the BeanFactory [DefaultListableBeanFactory] factory, use Used to generate Bean objects.
(2) Instantiate the BeanDefinitionReader annotation configuration reader, which is used to read and convert classes with specific annotations (such as @Service, @Repository) into BeanDefinition objects (BeanDefinition is an extremely important concept in Spring, which stores beans All characteristic information of the object, such as whether it is a singleton, whether it is lazy loaded, factoryBeanName, etc.)
(3) Instantiate the ClassPathBeanDefinitionScanner path scanner, which is used to scan the specified package directory to find bean objects.
complete process
- this() call
- this() will call the no-argument constructor of AnnotationConfigApplicationContext, and in Java inheritance, the constructor of the parent class will be called first. Therefore, the construction method of the parent class GeniricApplicationContext of AnnotationConfigApplicationContext will be called first, and the beanFactory will be initialized in the parent class, that is, a DefaultListableBeanFactory will be directly new.
public GenericApplicationContext() {
this.beanFactory = new DefaultListableBeanFactory();
}
- In this(), a Bean reader is instantiated through new AnnotatedBeanDefinitionReader(this), and a post-processor is added to the container.
- Added 2 beanFactory post processors to the container: ConfigurationClassPostProcessor and EventListenerMethodProcessor.
- Two bean postprocessors are added to the container: AutowiredAnnotationBeanPostProcessor and CommonAnnotationBeanPostProcessor.
- Add a common component to the container: DefaultEventListenerFactory.
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
this(registry, getOrCreateEnvironment(registry));
}
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
Assert.notNull(environment, "Environment must not be null");
this.registry = registry;
this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
public static void registerAnnotationConfigProcessors(BeanDefinitionRegistry registry) {
registerAnnotationConfigProcessors(registry, null);
}
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, @Nullable Object source) {
DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
if (beanFactory != null) {
if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
}
if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
}
}
Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
}
// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition();
try {
def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
AnnotationConfigUtils.class.getClassLoader()));
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
}
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
}
return beanDefs;
}
- Through new ClassPathBeanDefinitionScanner(this), a path scanner that can scan the package directory specified by the user to find bean objects is instantiated.
- register(annotatedClasses) parses the incoming configuration class annotatedClasses into BeanDefinition (the actual type is AnnotatedGenericBeanDefinition), and then puts it into BeanDefinitionMap, so that annotatedClasses can be parsed later in ConfigurationClassPostProcessor. At this time, it only registers BeanDefinition information without instantiation.
<T> void doRegisterBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier, @Nullable String name,
@Nullable Class<? extends Annotation>[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {
// 解析传入的配置类，实际上这个方法既可以解析配置类，也可以解析 Spring bean 对象
AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
// 判断是否需要跳过，判断依据是此类上有没有 @Conditional 注解
if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
return;
}
abd.setInstanceSupplier(instanceSupplier);
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
abd.setScope(scopeMetadata.getScopeName());
String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
// 处理类上的通用注解
AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
if (qualifiers != null) {
for (Class<? extends Annotation> qualifier : qualifiers) {
if (Primary.class == qualifier) {
abd.setPrimary(true);
}
else if (Lazy.class == qualifier) {
abd.setLazyInit(true);
}
else {
abd.addQualifier(new AutowireCandidateQualifier(qualifier));
}
}
}
// 封装成一个 BeanDefinitionHolder
for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
customizer.customize(abd);
}
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
// 处理 scopedProxyMode
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
// 把 BeanDefinitionHolder 注册到 registry
BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}
- Executing the refresh() method The refresh() method is the core of the entire Spring container. In this method, functions such as bean instantiation, initialization, automatic assembly, and AOP are performed.
Key method: AbstractApplicationContext.refresh( )
Above we know how to initialize an IOC container, so the next step is to make this IOC container really work: that is, first scan out the beans to be put into the container, wrap them into BeanDefinition objects, and then create beans through reflection , and complete the assignment operation, this is the simplest function of the IOC container. But looking at the picture above, it is obvious that Spring’s initialization process is much more than this. Let’s analyze the meaning of this design in detail:
If the user wants to do some custom operations after scanning the bean: suppose the container contains a and b , then dynamically inject c into the container, and inject d if it is not satisfied. This kind of operation is also supported by Spring. You can use the BeanFactoryPostProcessor post processor it provides, which corresponds to the invokeBeanFactoryPostProcessors operation in the above figure .
What if the user also wants to do some operations before and after the bean's initialization? For example, generating proxy objects, modifying object properties, etc., Spring provides us with a BeanPostProcessor post-processor. In fact, most of the functions in the Spring container are completed through the Bean post-processor. Spring also provides us with an add entry. Corresponding to the registerBeanPostProcessors operation in the above figure.
During the container creation process, if the user wants to monitor events such as container startup and refresh, do some custom operations based on these events? Spring has already considered it for us, providing an interface for adding a listener and a container event notification interface, corresponding to the registerListeners operation in the above figure.
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
// 1. 刷新前的预处理
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
// 2. 获取 beanFactory，即前面创建的【DefaultListableBeanFactory】
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
// 3. 预处理 beanFactory，向容器中添加一些组件
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
// 4. 子类通过重写这个方法可以在 BeanFactory 创建并与准备完成以后做进一步的设置
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
// 5. 执行 BeanFactoryPostProcessor 方法，beanFactory 后置处理器
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
// 6. 注册 BeanPostProcessors，bean 后置处理器
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
// 7. 初始化 MessageSource 组件（做国际化功能；消息绑定，消息解析）
initMessageSource();
// Initialize event multicaster for this context.
// 8. 初始化事件派发器，在注册监听器时会用到
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
// 9. 留给子容器（子类），子类重写这个方法，在容器刷新的时候可以自定义逻辑，web 场景下会使用
onRefresh();
// Check for listener beans and register them.
// 10. 注册监听器，派发之前步骤产生的一些事件（可能没有）
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
// 11. 初始化所有的非单实例 bean
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
// 12. 发布容器刷新完成事件
finishRefresh();
}
...
}
}
refresh() is mainly used to refresh the container. Each container in Spring will call the refresh() method to refresh. Whether it is the parent-child container of Spring or the feign isolation container in Spring Cloud Feign, each container will call this method to complete initialization. refresh() can be divided into the above 12 steps, and the more important steps will be described in detail below.
First summarize the main functions of each step of the refresh() method:
- Preprocessing before prepareRefresh() refresh:
- initPropertySources(): Initialize some property settings, subclasses customize personalized property setting methods;
- getEnvironment().validateRequiredProperties(): Verify the validity of properties
- earlyApplicationEvents = new LinkedHashSet(): save some early events in the container;
- obtainFreshBeanFactory(): Get the BeanFactory created when the container is initialized:
- refreshBeanFactory(): Refresh the BeanFactory and set the serialization ID;
- getBeanFactory(): Returns the BeanFactory object created by the GenericApplicationContext in initialization, namely the [DefaultListableBeanFactory] type
- prepareBeanFactory(beanFactory): BeanFactory preprocessing work, add some components to the container:
- Set the BeanFactory class loader, set the expression parser, etc.
- 添加BeanPostProcessor【ApplicationContextAwareProcessor】
- Set the interface that ignores automatic assembly: EnvironmentAware, EmbeddedValueResolverAware, ResourceLoaderAware, ApplicationEventPublisherAware, MessageSourceAware, ApplicationContextAware;
- Register auto-assembly classes that can be parsed, that is, they can be automatically injected through annotations in any component: BeanFactory, ResourceLoader, ApplicationEventPublisher, ApplicationContext
- 添加BeanPostProcessor【ApplicationListenerDetector】
- Add compile-time AspectJ;
- For the three components registered in BeanFactory: environment [ConfigurableEnvironment], systemProperties [Map<String, Object>], systemEnvironment [Map<String, Object>]
- postProcessBeanFactory(beanFactory): The subclass overrides this method, which can realize further settings after the BeanFactory is created and preprocessed.
- invokeBeanFactoryPostProcessors(beanFactory): The method of executing BeanFactoryPostProcessor after BeanFactory standard initialization, that is, the post-processor of BeanFactory:
- 先执行BeanDefinitionRegistryPostProcessor： postProcessor.postProcessBeanDefinitionRegistry(registry)
- Get all the collections that implement the BeanDefinitionRegistryPostProcessor interface type
- First execute the BeanDefinitionRegistryPostProcessor that implements the PriorityOrdered priority interface
- Then execute the BeanDefinitionRegistryPostProcessor that implements the Ordered sequence interface
- Finally, execute BeanDefinitionRegistryPostProcessors that do not implement any priority or sequence interface
- Then execute the BeanFactoryPostProcessor method: postProcessor.postProcessBeanFactory(beanFactory)
- Get all the collections that implement the BeanFactoryPostProcessor interface type
- First execute the BeanFactoryPostProcessor that implements the PriorityOrdered priority interface
- Then execute the BeanFactoryPostProcessor that implements the Ordered sequence interface
- Finally execute the BeanFactoryPostProcessor that does not implement any priority or sequence interface
- 先执行BeanDefinitionRegistryPostProcessor： postProcessor.postProcessBeanDefinitionRegistry(registry)
- registerBeanPostProcessors(beanFactory): Register BeanPostProcessor, the post-processor of Bean in the container, its main function is to intervene in the process of Spring initialization bean, so as to complete functions such as proxy, automatic injection, circular dependency, etc.
- Get the collection of all types that implement the BeanPostProcessor interface:
- First register the BeanPostProcessor that implements the PriorityOrdered priority interface;
- Then register the BeanPostProcessor that implements the Ordered priority interface;
- Finally, register the BeanPostProcessor that does not implement any priority interface;
- Finally register the BeanPostProcessor of MergedBeanDefinitionPostProcessor type: beanFactory.addBeanPostProcessor(postProcessor);
- Register an ApplicationListenerDetector for the container: it is used to check whether it is an ApplicationListener after the Bean is created. If it is, put the Bean in the container and save it: applicationContext.addApplicationListener((ApplicationListener<?>) bean); 6 default BeanProcessors (without any proxy mode)
- initMessageSource(): Initialize the MessageSource component, which is mainly used for internationalization, message binding and message parsing:
- initApplicationEventMulticaster(): Initialize the event dispatcher, which will be used when registering the listener
- See if there is a custom ApplicationEventMulticaster in the BeanFactory container: if so, get it directly from the container; if not, create a SimpleApplicationEventMulticaster
- Add the created ApplicationEventMulticaster to the BeanFactory, and other components can be injected directly and automatically in the future.
- onRefresh(): Leave it to sub-containers and sub-classes to override this method, and you can customize the logic when the container is refreshed.
- registerListeners(): Register listeners: Register all ApplicationListeners in the container to the event dispatcher, and dispatch the events generated by the previous steps:
- finishBeanFactoryInitialization(beanFactory): Initialize all remaining single instance beans, the core method is preInstantiateSingletons(), which will call the getBean() method to create objects;
- Get all beanDefinitionNames in the container, initialize and create objects in turn
- Obtain the bean definition information RootBeanDefinition, which represents the merged object of its own BeanDefinition and the BeanDefinition that may have a parent class
- If the bean meets these three conditions: non-abstract, single instance, and non-lazy loading, execute the singleton bean creation process:
- After all Beans are created using getBean(), check whether all Beans are SmartInitializingSingleton interface, if so; execute afterSingletonsInstantiated();
- finishRefresh(): Publish the BeanFactory container refresh completion event:
- nitLifecycleProcessor(): Initialize post-processors related to the life cycle: by default, find out whether there is a lifecycleProcessor component [LifecycleProcessor] from the container, if not, create a DefaultLifecycleProcessor() and add it to the container;
- getLifecycleProcessor().onRefresh(): Get the previously defined lifecycle processor (LifecycleProcessor) callback onRefresh() method
- publishEvent(new ContextRefreshedEvent(this)): publish container refresh completion event;
- liveBeansView.registerApplicationContext(this);
Let's take a look at the source code of the key methods marked in red above
Preprocessing of BeanFactory
org.springframework.context.support.AbstractApplicationContext#prepareBeanFactory
As the name suggests, this interface is to add some built-in components to the beanFactory factory, preprocessing process.
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
// 设置 classLoader
beanFactory.setBeanClassLoader(getClassLoader());
//设置 bean 表达式解析器
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
// 添加一个 BeanPostProcessor【ApplicationContextAwareProcessor】
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
// 设置忽略自动装配的接口，即不能通过注解自动注入
beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
// 注册可以解析的自动装配类，即可以在任意组件中通过注解自动注入
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// Register early post-processor for detecting inner beans as ApplicationListeners.
// 添加一个 BeanPostProcessor【ApplicationListenerDetector】
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// Detect a LoadTimeWeaver and prepare for weaving, if found.
// 添加编译时的 AspectJ
if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
// Set a temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
// Register default environment beans.
// 注册 environment 组件，类型是【ConfigurableEnvironment】
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
// 注册 systemProperties 组件，类型是【Map<String, Object>】
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
// 注册 systemEnvironment 组件，类型是【Map<String, Object>】
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
}
Execute the post processor of BeanFactory
org.springframework.context.support.PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors
When Spring scans all beans and converts them into BeanDefinition, we can do some custom operations, thanks to the BeanFactoryPostProcessor interface provided by Spring.
Among them, BeanFactoryPostProcessor has a sub-interface BeanDefinitionRegistryPostProcessor. The former will expose ConfigurableListableBeanFactory to us, and the latter will expose the BeanDefinitionRegistry register to us. Once we get the register, we can inject it on demand, for example, to solve this demand: Assuming that the container contains a and b, then dynamically inject c into the container, and inject d if it is not satisfied.
At the same time, Spring allows us to control the order of components of the same type, such as the @Order annotation we commonly use in AOP. Of course, the BeanFactoryPostProcessor interface here also provides the order. The implementation class that implements the PriorityOrdered interface is the first to be executed, and then to The implementation class that implements the Ordered interface, and finally the remaining regular BeanFactoryPostProcessor class.
At this time, look at the above picture again, do you find it relatively simple? First, the postProcessBeanDefinitionRegistry() method will be called back, and then the postProcessBeanFactory() method will be called back. Finally, just pay attention to the order. Let’s take a look at the specific code implementation.
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// beanFactoryPostProcessors 这个参数是指用户通过 AnnotationConfigApplicationContext.addBeanFactoryPostProcessor() 方法手动传入的 BeanFactoryPostProcessor，没有交给 spring 管理
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
// 代表执行过的 BeanDefinitionRegistryPostProcessor
Set<String> processedBeans = new HashSet<>();
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
// 常规后置处理器集合，即实现了 BeanFactoryPostProcessor 接口
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
// 注册后置处理器集合，即实现了 BeanDefinitionRegistryPostProcessor 接口
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
// 处理自定义的 beanFactoryPostProcessors（指调用 context.addBeanFactoryPostProcessor() 方法），一般这里都没有
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
// 调用 postProcessBeanDefinitionRegistry 方法
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// Separate between BeanDefinitionRegistryPostProcessors that implement
// PriorityOrdered, Ordered, and the rest.
// 定义一个变量 currentRegistryProcessors，表示当前要处理的 BeanFactoryPostProcessors
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
// 首先，从容器中查找实现了 PriorityOrdered 接口的 BeanDefinitionRegistryPostProcessor 类型，这里只会查找出一个【ConfigurationClassPostProcessor】
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 判断是否实现了 PriorityOrdered 接口
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
// 添加到 currentRegistryProcessors
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
// 添加到 processedBeans，表示已经处理过这个类了
processedBeans.add(ppName);
}
}
// 设置排列顺序
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 添加到 registry 中
registryProcessors.addAll(currentRegistryProcessors);
// 执行 [postProcessBeanDefinitionRegistry] 回调方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
// 将 currentRegistryProcessors 变量清空，下面会继续用到
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
// 接下来，从容器中查找实现了 Ordered 接口的 BeanDefinitionRegistryPostProcessors 类型，这里可能会查找出多个
// 因为【ConfigurationClassPostProcessor】已经完成了 postProcessBeanDefinitionRegistry() 方法，已经向容器中完成扫描工作，所以容器会有很多个组件
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 判断 processedBeans 是否处理过这个类，且是否实现 Ordered 接口
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
// 设置排列顺序
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 添加到 registry 中
registryProcessors.addAll(currentRegistryProcessors);
// 执行 [postProcessBeanDefinitionRegistry] 回调方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
// 将 currentRegistryProcessors 变量清空，下面会继续用到
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
// 最后，从容器中查找剩余所有常规的 BeanDefinitionRegistryPostProcessors 类型
boolean reiterate = true;
while (reiterate) {
reiterate = false;
// 根据类型从容器中查找
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
// 判断 processedBeans 是否处理过这个类
if (!processedBeans.contains(ppName)) {
// 添加到 currentRegistryProcessors
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
// 添加到 processedBeans，表示已经处理过这个类了
processedBeans.add(ppName);
// 将标识设置为 true，继续循环查找，可能随时因为防止下面调用了 invokeBeanDefinitionRegistryPostProcessors() 方法引入新的后置处理器
reiterate = true;
}
}
// 设置排列顺序
sortPostProcessors(currentRegistryProcessors, beanFactory);
// 添加到 registry 中
registryProcessors.addAll(currentRegistryProcessors);
// 执行 [postProcessBeanDefinitionRegistry] 回调方法
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
// 将 currentRegistryProcessors 变量清空，因为下一次循环可能会用到
currentRegistryProcessors.clear();
}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
// 现在执行 registryProcessors 的 [postProcessBeanFactory] 回调方法
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
// 执行 regularPostProcessors 的 [postProcessBeanFactory] 回调方法，也包含用户手动调用 addBeanFactoryPostProcessor() 方法添加的 BeanFactoryPostProcessor
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// 从容器中查找实现了 BeanFactoryPostProcessor 接口的类
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
// 表示实现了 PriorityOrdered 接口的 BeanFactoryPostProcessor
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
// 表示实现了 Ordered 接口的 BeanFactoryPostProcessor
List<String> orderedPostProcessorNames = new ArrayList<>();
// 表示剩下来的常规的 BeanFactoryPostProcessors
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
// 判断是否已经处理过，因为 postProcessorNames 其实包含了上面步骤处理过的 BeanDefinitionRegistry 类型
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
// 判断是否实现了 PriorityOrdered 接口
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
// 判断是否实现了 Ordered 接口
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
// 剩下所有常规的
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
// 先将 priorityOrderedPostProcessors 集合排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 执行 priorityOrderedPostProcessors 的 [postProcessBeanFactory] 回调方法
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
// 接下来，把 orderedPostProcessorNames 转成 orderedPostProcessors 集合
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
// 将 orderedPostProcessors 集合排序
sortPostProcessors(orderedPostProcessors, beanFactory);
// 执行 orderedPostProcessors 的 [postProcessBeanFactory] 回调方法
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
// 最后把 nonOrderedPostProcessorNames 转成 nonOrderedPostProcessors 集合，这里只有一个，myBeanFactoryPostProcessor
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
// 执行 nonOrderedPostProcessors 的 [postProcessBeanFactory] 回调方法
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
// 清除缓存
beanFactory.clearMetadataCache();
}
Process summary
（1）先执行BeanDefinitionRegistryPostProcessor： postProcessor.postProcessBeanDefinitionRegistry(registry)
① 获取所有的实现了BeanDefinitionRegistryPostProcessor接口类型的集合
② 先执行实现了PriorityOrdered优先级接口的BeanDefinitionRegistryPostProcessor
③ 再执行实现了Ordered顺序接口的BeanDefinitionRegistryPostProcessor
④ 最后执行没有实现任何优先级或者是顺序接口的BeanDefinitionRegistryPostProcessors
（2）再执行BeanFactoryPostProcessor的方法：postProcessor.postProcessBeanFactory(beanFactory)
① 获取所有的实现了BeanFactoryPostProcessor接口类型的集合
② 先执行实现了PriorityOrdered优先级接口的BeanFactoryPostProcessor
③ 再执行实现了Ordered顺序接口的BeanFactoryPostProcessor
④ 最后执行没有实现任何优先级或者是顺序接口的BeanFactoryPostProcessor
Register the bean's post-processor
org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors
This step is to inject the BeanPostProcessor post-processor into the container. Note that this is only injected into the container rather than used. Regarding BeanPostProcessor, its main function is to intervene in the process of Spring initialization bean, so as to complete various functions such as proxy, automatic injection, and circular dependency.
public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
// 从容器中获取 BeanPostProcessor 类型
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
// Register BeanPostProcessorChecker that logs an info message when
// a bean is created during BeanPostProcessor instantiation, i.e. when
// a bean is not eligible for getting processed by all BeanPostProcessors.
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
// 向容器中添加【BeanPostProcessorChecker】，主要是用来检查是不是有 bean 已经初始化完成了，
// 如果没有执行所有的 beanPostProcessor（用数量来判断），如果有就会打印一行 info 日志
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
// Separate between BeanPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
// 存放实现了 PriorityOrdered 接口的 BeanPostProcessor
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
// 存放 MergedBeanDefinitionPostProcessor 类型的 BeanPostProcessor
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
// 存放实现了 Ordered 接口的 BeanPostProcessor 的 name
List<String> orderedPostProcessorNames = new ArrayList<>();
// 存放剩下来普通的 BeanPostProcessor 的 name
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
// 从 beanFactory 中查找 postProcessorNames 里的 bean，然后放到对应的集合中
for (String ppName : postProcessorNames) {
// 判断有无实现 PriorityOrdered 接口
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
// 如果实现了 PriorityOrdered 接口，且属于 MergedBeanDefinitionPostProcessor
if (pp instanceof MergedBeanDefinitionPostProcessor) {
// 把 MergedBeanDefinitionPostProcessor 类型的添加到 internalPostProcessors 集合中
internalPostProcessors.add(pp);
}
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, register the BeanPostProcessors that implement PriorityOrdered.
// 给 priorityOrderedPostProcessors 排序
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 先注册实现了 PriorityOrdered 接口的 beanPostProcessor
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// Next, register the BeanPostProcessors that implement Ordered.
// 从 beanFactory 中查找 orderedPostProcessorNames 里的 bean，然后放到对应的集合中
List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String ppName : orderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
orderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 给 orderedPostProcessors 排序
sortPostProcessors(orderedPostProcessors, beanFactory);
// 再注册实现了 Ordered 接口的 beanPostProcessor
registerBeanPostProcessors(beanFactory, orderedPostProcessors);
// Now, register all regular BeanPostProcessors.
List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String ppName : nonOrderedPostProcessorNames) {
BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
nonOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {
internalPostProcessors.add(pp);
}
}
// 再注册常规的 beanPostProcessor
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
// Finally, re-register all internal BeanPostProcessors.
// 排序 MergedBeanDefinitionPostProcessor 这种类型的 beanPostProcessor
sortPostProcessors(internalPostProcessors, beanFactory);
// 最后注册 MergedBeanDefinitionPostProcessor 类型的 beanPostProcessor
registerBeanPostProcessors(beanFactory, internalPostProcessors);
// Re-register post-processor for detecting inner beans as ApplicationListeners,
// moving it to the end of the processor chain (for picking up proxies etc).
// 给容器中添加【ApplicationListenerDetector】 beanPostProcessor，判断是不是监听器，如果是就把 bean 放到容器中保存起来
// 此时容器中默认会有 6 个内置的 beanPostProcessor
// 0 = {ApplicationContextAwareProcessor@1632}
// 1 = {ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor@1633}
// 2 = {PostProcessorRegistrationDelegate$BeanPostProcessorChecker@1634}
// 3 = {CommonAnnotationBeanPostProcessor@1635}
// 4 = {AutowiredAnnotationBeanPostProcessor@1636}
// 5 = {ApplicationListenerDetector@1637}
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
Initialize the event dispatcher
org.springframework.context.support.AbstractApplicationContext#initApplicationEventMulticaster:
During the entire container creation process, Spring will publish many container events, such as container startup, refresh, shutdown, etc. The realization of this function benefits from the ApplicationEventMulticaster broadcaster component here, through It dispatches event notifications.
protected void initApplicationEventMulticaster() {
// 获取 beanFactory
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
// 看看容器中是否有自定义的 applicationEventMulticaster
if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) {
// 有就从容器中获取赋值
this.applicationEventMulticaster =
beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class);
if (logger.isTraceEnabled()) {
logger.trace("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]");
}
}
else {
// 没有，就创建一个 SimpleApplicationEventMulticaster
this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
// 将创建的 ApplicationEventMulticaster 添加到 BeanFactory 中， 其他组件就可以自动注入了
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
if (logger.isTraceEnabled()) {
logger.trace("No '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "' bean, using " +
"[" + this.applicationEventMulticaster.getClass().getSimpleName() + "]");
}
}
}
Register ApplicationListener listener
org.springframework.context.support.AbstractApplicationContext#registerListeners:
This step is mainly to register all ApplicationListeners in the container to the event dispatcher and dispatch the events generated in the previous steps.
protected void registerListeners() {
// Register statically specified listeners first.
// 获取之前步骤中保存的 ApplicationListener
for (ApplicationListener<?> listener : getApplicationListeners()) {
// getApplicationEventMulticaster() 就是获取之前步骤初始化的 applicationEventMulticaster
getApplicationEventMulticaster().addApplicationListener(listener);
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let post-processors apply to them!
// 从容器中获取所有的 ApplicationListener
String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
for (String listenerBeanName : listenerBeanNames) {
getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
}
// Publish early application events now that we finally have a multicaster...
// 派发之前步骤产生的 application events
Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
this.earlyApplicationEvents = null;
if (earlyEventsToProcess != null) {
for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
getApplicationEventMulticaster().multicastEvent(earlyEvent);
}
}
}
Initialize all singleton beans
org.springframework.beans.factory.support.DefaultListableBeanFactory#preInstantiateSingletons:
In the previous steps, most of Spring’s components have been initialized, and the remaining step is to initialize all remaining single instance beans. Spring mainly uses preInstantiateSingletons The () method initializes all the beans in the container. Here we will not go into details about the Bean creation process.
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
// 获取容器中的所有 beanDefinitionName
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
// 循环进行初始化和创建对象
for (String beanName : beanNames) {
// 获取 RootBeanDefinition，它表示自己的 BeanDefinition 和可能存在父类的 BeanDefinition 合并后的对象
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
// 如果是非抽象的，且单实例，非懒加载
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
// 如果是 factoryBean，利用下面这种方法创建对象
if (isFactoryBean(beanName)) {
// 如果是 factoryBean，则 加上 &，先创建工厂 bean
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {
final FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
// 不是工厂 bean，用这种方法创建对象
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
// 检查所有的 bean 是否是 SmartInitializingSingleton 接口
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
// 回调 afterSingletonsInstantiated() 方法，可以在回调中做一些事情
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
Publish the BeanFactory container refresh complete event
**org.springframework.context.support.AbstractApplicationContext#finishRefresh:
** After the entire container is initialized, some finishing work will be done here, such as cleaning the cache, initializing the lifecycle processor, publishing container refresh events, etc.
protected void finishRefresh() {
// Clear context-level resource caches (such as ASM metadata from scanning).
// 清理缓存
clearResourceCaches();
// Initialize lifecycle processor for this context.
// 初始化和生命周期有关的后置处理器
initLifecycleProcessor();
// Propagate refresh to lifecycle processor first.
// 拿到前面定义的生命周期处理器【LifecycleProcessor】回调 onRefresh() 方法
getLifecycleProcessor().onRefresh();
// Publish the final event.
// 发布容器刷新完成事件
publishEvent(new ContextRefreshedEvent(this));
// Participate in LiveBeansView MBean, if active.
LiveBeansView.registerApplicationContext(this);
}