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Spring启动和Bean创建过程中的可扩展接口

Spring中有一些可以扩展的接口，可以用来在工作中更深度的使用Spring，这些接口大多分布在AbstractApplicationContext.refresh() 和 AbstractAutowireCapableBeanFactory.createBean()这两个方法的执行过程中。

2.AbstractApplicationContext.refresh()

2.1 refresh()简介

AbstractApplicationContext.refresh()是Spring环境启动过程中的一个重要方法，此方法中实例化了所有的bean， 任何ApplicationContext的实现，都需要调用此方法 。

如上图所示，Spring中，所有的ApplicationContext，都继承于AbstractApplicationContext。

为节省篇幅，仅将要分析的几个方法代码片段抽取出来，refresh()的全部实现可查看源码中的AbstractApplicationContext.refresh()方法。

// 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);

// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);

// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);

// Initialize event multicaster for this context.
initApplicationEventMulticaster();

// Check for listener beans and register them.
registerListeners();
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2.2 prepareRefresh()

调用了initPropertySources,初始化资源，如属性文件中的占位符等。由子类实现，如AbstractRefreshableWebApplicationContext。

2.3 obtainFreshBeanFactory()

获取ConfigurableListableBeanFactory:

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	refreshBeanFactory();
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (logger.isDebugEnabled()) {
		logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
	}
	return beanFactory;
}
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此方法中主要执行两部分流程：

2.3.1 调用refreshBeanFactory()

调用抽象方法refreshBeanFactory()，由子类AbstractRefreshableApplicationContext实现，代码片段如下：

DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory);  //读取xml,注册BeanDefinition。
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loadBeanDefinitions是AbstractRefreshableApplicationContext的一个抽象方法，由其子类AbstractXmlApplicationContext实现，详细了解AbstractXmlApplicationContext可参考 Spring自定义配置的源码解析与实现

2.3.2 调用getBeanFactory()

调用抽象方法getBeanFactory()，由子类AbstractRefreshableApplicationContext实现，返回一个接口ConfigurableListableBeanFactory的实现类DefaultListableBeanFactory的实例。

这个DefaultListableBeanFactory实例，由上面的refreshBeanFactory()中调用createBeanFactory()创建。

2.4 prepareBeanFactory

配置ConfigurableListableBeanFactory。

ConfigurableListableBeanFactory继承了BeanFactory，实现类是DefaultListableBeanFactory。

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory){....}

2.4.1 设置classLoader:

beanFactory.setBeanClassLoader(getClassLoader());

通过org.springframework.util.ClassUtils.getDefaultClassLoader()获取ClassLoader。

2.4.2 创建ApplicationContextAwareProcessor

beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

创建ApplicationContextAwareProcessor对象，并且添加到DefaultListableBeanFactory中。

ApplicationContextAwareProcessor实现了BeanPostProcessor，并在实现的BeanPostProcessor.postProcessBeforeInitialization中，定义了对一些列对org.springframework.beans.factory.Aware子接口的处理。

注：这里只是添加了BeanPostProcessor，但并未执行。

private void invokeAwareInterfaces(Object bean) {
    if (bean instanceof Aware) {
		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);
		}
	}
}
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在后续创建Bean的流程中，会执行所有的BeanPostProcessor，也就是会执行ApplicationContextAwareProcessor.postProcessBeforeInitialization设置各种Aware接口。

2.4.3 设置默认的上下文bean

注册Spring自身使用的一些Bean：

// Register default environment beans.
		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());
		}
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其中：

String ENVIRONMENT_BEAN_NAME = "environment";
String SYSTEM_PROPERTIES_BEAN_NAME = "systemProperties";
String SYSTEM_ENVIRONMENT_BEAN_NAME = "systemEnvironment";
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2.5 invokeBeanFactoryPostProcessors

调用所有的 BeanFactoryPostProcessor.postProcessBeanFactory。 PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

public static void invokeBeanFactoryPostProcessors(
			ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors){....}
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2.6 registerBeanPostProcessors

注册所有的BeanPostProcessor

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
	}
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2.7 initApplicationEventMulticaster

初始化ApplicationEventMulticaster，实现类是SimpleApplicationEventMulticaster。

this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
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public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";

2.8 registerListeners

向ApplicationEventMulticaster注册ApplicationListner。

/**
	 * Add beans that implement ApplicationListener as listeners.
	 * Doesn't affect other listeners, which can be added without being beans.
	 */
	protected void registerListeners() {
		// Register statically specified listeners first.
		for (ApplicationListener<?> listener : getApplicationListeners()) {
			getApplicationEventMulticaster().addApplicationListener(listener);
		}

		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let post-processors apply to them!
		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...
		Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
		this.earlyApplicationEvents = null;
		if (earlyEventsToProcess != null) {
			for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
				getApplicationEventMulticaster().multicastEvent(earlyEvent);
			}
		}
	}
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3 AbstractAutowireCapableBeanFactory.createBean()

3.1 DefaultListableBeanFactory

如上图所示， DefaultListableBeanFactory

是ListableBeanFactory和BeanDefinitionRegistry的默认实现，是所有BeanFactory的始祖。最终创建bean的，是它的直接父类AbstractAutowireCapableBeanFactory.createBean 。

3.2 createBean

protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {....}

主要执行了两个方法：

Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
Object beanInstance = doCreateBean(beanName, mbdToUse, args);

3.3 AbstractAutowireCapableBeanFactory.doCreateBean

3.3.1 createBeanInstance

BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) 主要做了以下工作：

Class<?> beanClass = resolveBeanClass(mbd, beanName);
BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd)
getInstantiationStrategy().instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner)

3.3.2 populateBean

populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) 根据BeanDefinition为BeanWrapper封装的bean代理对象设置属性值。设置的方式，是创建了BeanDefinitionValueResolver对象，并BeanDefinitionValueResolver.resolveValueIfNecessary实现。resolveValueIfNecessary执行了一系列判断和递归调用，将属性值填充。

3.3.3 initializeBean

Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd)

1 invokeAwareMethods : 执行 BeanNameAware , BeanClassLoaderAware , BeanFactoryAware
2 applyBeanPostProcessorsBeforeInitialization: 调用了所有 BeanPostProcessor的postProcessBeforeInitialization 方法。
3 invokeInitMethods:
- 1）执行 InitializingBean.afterPropertiesSet ；
- 2）执行 init-method;
4 applyBeanPostProcessorsAfterInitialization: 执行所有的 BeanPostProcessor 的 postProcessAfterInitialization 方法。

3.3.4 registerDisposableBeanIfNecessary

注册Bean销毁事件。 protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd)

1 执行 DisposableBean.destroy() ;
2 执行destroy-method；

4 总结

4.1 **Aware

实现**Aware类的接口，用于获取到Spring环境中的各种信息或对象：

常用的有：

ApplicationContextAware：获取当前的ApplicationContext；
BeanNameAware：获取当前的beanName;
BeanClassLoaderAware：获取当前的ClassLoader;
BeanFactoryAware：获取当前的BeanFactory;
ApplicationEventPublisherAware：获取当前的ApplicationEventPublisher，用于发布事件；要接收事件的类可以实现ApplicationListener接口，并实现其中的onApplicationEvent方法。

其他还有：