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

注册时机

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BeanNameAwareBeanClassLoaderAwareBeanFactoryAware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);
			}
		}
	}
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