Spring源码之四prepareBeanFactory()方法

大家好，我是程序员田同学！

今天带大家解读refresh()方法的第三个方法prepareBeanFactory()，通过对refresh()的一步步解读，想必有一天小伙伴们能揭开Spring的神秘面纱。

照例，先站在prepareBeanFactory()的门外看它都做了什么，然后再逐步深入剖析。prepareBeanFactory()方法主要是：

设置 BeanFactory 的类加载器，添加 BeanPostProcessor，手动注册几个特殊的 bean。

扩展：BeanPostProcessor是Spring IOC容器给我们提供的一个扩展接口。

//bean初始化方法调用前被调用
	@Nullable
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}
	
	//bean初始化方法调用后被调用
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

BeanPostProcessor在整个bean的生命周期中处于红色箭头所示的位置。

prepareBeanFactory()的每个详细方法在以下代码注释中。

// Tell the internal bean factory to use the context's class loader etc.
	//设置上下文环境的启动类加载器
	beanFactory.setBeanClassLoader(getClassLoader());

	//添加bean表达式解释器，为了能够让我们的beanFactory去解析bean表达式
	beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));

	//spring内部的属性编辑器、既读取配置文件
	beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

	// Configure the bean factory with context callbacks.
	//添加BeanPostProcessor
	beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

	//跳过以下6个属性的自动注入
	//因为在ApplicationContextAwareProcessor后置处理器中通过setter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.

	////注册四个特殊的bean
	//在应用代码就可以通过类型自动装配把工厂实例和ApplicationContext实例设置到自定义bean的属性中
	//这四个属性都会被自动设置，虽然没有在显示的在bean定义xml中注入它们
	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.
	//注册事件监听器
	beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));


	// Detect a LoadTimeWeaver and prepare for weaving, if found.
	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.
	// 如果没有定义 "environment" 这个 bean，那么 Spring 会 "手动" 注册一个
	if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
		beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
	}
	// 如果没有定义 "systemProperties" 这个 bean，那么 Spring 会 "手动" 注册一个
	if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
		beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
	}
	// 如果没有定义 "systemEnvironment" 这个 bean，那么 Spring 会 "手动" 注册一个
	if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
		beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
	}