Spring系列-3.2 ApplicationContextAwareProcessor
Spring版本：Spring 5.2.9.BUILD-SNAPSHOT
修改过部分源码，但不影响主体流程
概述
ApplicationContextAwareProcessor用来完成以下功能：向某些实现了Aware的接口的bean设置ApplicationContext中的相应属性。
-
EnvironmentAware -
EmbeddedValueResolverAware -
ResourceLoaderAware -
ApplicationEventPublisherAware -
MessageSourceAware -
ApplicationContextAware
继承关系
注册时机
在AbstractApplicationContext#prepareBeanFactory方法进行注册
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
// 设置beanFactory的classloader为当前context的classloader
beanFactory.setBeanClassLoader(getClassLoader());
// 设置beanfactory的表达式语言处理器
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
// 为beanFactory增加一个默认的propertyEditor，这个主要是对bean的属性等设置管理的一个工具类
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
// 添加beanPostProcessor,ApplicationContextAwareProcessor此类用来完成某些Aware对象的注入
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
// 设置要忽略自动装配的接口，很多同学理解不了为什么此处要对这些接口进行忽略，原因非常简单，这些接口的实现是由容器通过set方法进行注入的，
// 所以在使用autowire进行注入的时候需要将这些接口进行忽略
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.
// 设置几个自动装配的特殊规则,当在进行ioc初始化的如果有多个实现，那么就使用指定的对象进行注入
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.
// 注册BPP
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// Detect a LoadTimeWeaver and prepare for weaving, if found.
// 增加对AspectJ的支持，在java中织入分为三种方式，分为编译器织入，类加载器织入，运行期织入，编译器织入是指在java编译器，采用特殊的编译器，将切面织入到java类中，
// 而类加载期织入则指通过特殊的类加载器，在类字节码加载到JVM时，织入切面，运行期织入则是采用cglib和jdk进行切面的织入
// aspectj提供了两种织入方式，第一种是通过特殊编译器，在编译器，将aspectj语言编写的切面类织入到java类中，第二种是类加载期织入，就是下面的load time weaving，此处后续讲
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.
// 注册默认的系统环境bean到一级缓存中
if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
}
if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
}
if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
}
}
调用时机
初始化bean实例时通过wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName)调用。
/**
* 初始化给定的bean实例，应用工厂回调以及init方法和BeanPostProcessors
*
* Initialize the given bean instance, applying factory callbacks
* as well as init methods and bean post processors.
* <p>Called from {@link #createBean} for traditionally defined beans,
* and from {@link #initializeBean} for existing bean instances.
* @param beanName the bean name in the factory (for debugging purposes)
* @param bean the new bean instance we may need to initialize
* @param mbd the bean definition that the bean was created with
* (can also be {@code null}, if given an existing bean instance)
* @return the initialized bean instance (potentially wrapped)
* @see BeanNameAware
* @see BeanClassLoaderAware
* @see BeanFactoryAware
* @see #applyBeanPostProcessorsBeforeInitialization
* @see #invokeInitMethods
* @see #applyBeanPostProcessorsAfterInitialization
*/
protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
// 如果安全管理器不为空
if (System.getSecurityManager() != null) {
// 以特权的方式执行回调bean中的Aware接口方法
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
invokeAwareMethods(beanName, bean);
return null;
}, getAccessControlContext());
}
else {
// Aware接口处理器，调用BeanNameAware、BeanClassLoaderAware、beanFactoryAware
invokeAwareMethods(beanName, bean);
}
Object wrappedBean = bean;
//如果mdb不为null || mbd不是"synthetic"。一般是指只有AOP相关的prointCut配置或者Advice配置才会将 synthetic设置为true
if (mbd == null || !mbd.isSynthetic()) {
// 将BeanPostProcessors应用到给定的现有Bean实例，调用它们的postProcessBeforeInitialization初始化方法。
// 返回的Bean实例可能是原始Bean包装器
wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
}
try {
//调用初始化方法，先调用bean的InitializingBean接口方法，后调用bean的自定义初始化方法
invokeInitMethods(beanName, wrappedBean, mbd);
}
catch (Throwable ex) {
//捕捉调用初始化方法时抛出的异常，重新抛出Bean创建异常：调用初始化方法失败
throw new BeanCreationException(
(mbd != null ? mbd.getResourceDescription() : null),
beanName, "Invocation of init method failed", ex);
}
//如果mbd为null || mbd不是"synthetic"
if (mbd == null || !mbd.isSynthetic()) {
// 将BeanPostProcessors应用到给定的现有Bean实例，调用它们的postProcessAfterInitialization方法。
// 返回的Bean实例可能是原始Bean包装器
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
}
//返回包装后的Bean
return wrappedBean;
}
源码解析
该类重写了postProcessBeforeInitialization方法，说明是在调用初始化方法之前再对bean内容进行修改。
/**
* 接口beanPostProcessor规定的方法，会在bean创建时，实例化后，初始化前，对bean对象应用
* @param bean the new bean instance
* @param beanName the name of the bean
* @return
* @throws BeansException
*/
@Override
@Nullable
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){
return bean;
}
AccessControlContext acc = null;
if (System.getSecurityManager() != null) {
acc = this.applicationContext.getBeanFactory().getAccessControlContext();
}
if (acc != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
// 检测bean上是否实现了某个aware接口，有的话进行相关的调用
invokeAwareInterfaces(bean);
return null;
}, acc);
}
else {
invokeAwareInterfaces(bean);
}
return bean;
}
invokeAwareInterfaces(Object bean)
/**
* 如果某个bean实现了某个aware接口，给指定的bean设置相应的属性值
*
* @param bean
*/
private void invokeAwareInterfaces(Object bean) {
if (bean instanceof EnvironmentAware) {
((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
}
if (bean instanceof EmbeddedValueResolverAware) {
((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
}
if (bean instanceof ResourceLoaderAware) {
((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
}
if (bean instanceof ApplicationEventPublisherAware) {
((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
}
if (bean instanceof MessageSourceAware) {
((MessageSourceAware) bean).setMessageSource(this.applicationContext);
}
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
}
invokeAwareMethods(beanName, bean)
该方法会处理调用BeanNameAware、BeanClassLoaderAware、BeanFactoryAware的方法，通过initializeBean方法调用执行，不通过ApplicationContextAwareProcessor处理。
/**
* 回调 bean 中 Aware接口 方法
* @param beanName
* @param bean
*/
private void invokeAwareMethods(String beanName, Object bean) {
//如果 bean 是 Aware 实例
if (bean instanceof Aware) {
//如果bean是BeanNameAware实例
if (bean instanceof BeanNameAware) {
//调用 bean 的setBeanName方法
((BeanNameAware) bean).setBeanName(beanName);
}
//如果bean是 BeanClassLoaderAware 实例
if (bean instanceof BeanClassLoaderAware) {
//获取此工厂的类加载器以加载Bean类(即使无法使用系统ClassLoader,也只能为null)
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
//调用 bean 的 setBeanClassLoader 方法
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
//如果bean是 BeanFactoryAware 实例
if (bean instanceof BeanFactoryAware) {
// //调用 bean 的 setBeanFactory 方法
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}
