Spring源码深度解析-IOC的初始化过程之refresh()--prepareBeanFactory--BeanPostProcessors

本篇文章我们分析一下Spring源码中refresh()--prepareBeanFactory以下两个方法。

beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

首先我们可以看到在prepareBeanFactory这个方法里面有多个addBeanPostProcessor方法的调用。以下是源码，可以发现是存的一个BeanPostProcessor接口实现类的数组；说明ApplicationContextAwareProcessor这个类和ApplicationListenerDetector类是BeanPostProcessor的实现类。

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {


	/** BeanPostProcessors to apply in createBean */
	private final List beanPostProcessors = new ArrayList<>();
}

我们接着去看一下BeanPostProcessor接口是什么东西。以下是源码，其实我们从名称里面就大概知道是什么意思。就是对象初始化途中，必须会经过这两个方法。那么这两个方法是做什么用的。我们接着往下看

public interface BeanPostProcessor {

	/**
	 * Apply this BeanPostProcessor to the given new bean instance before any bean
	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
	 * or a custom init-method). The bean will already be populated with property values.
	 * The returned bean instance may be a wrapper around the original.
	 * 
The default implementation returns the given {@code bean} as-is.
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if {@code null}, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 */
	@Nullable
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

	/**
	 * Apply this BeanPostProcessor to the given new bean instance after any bean
	 * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
	 * or a custom init-method). The bean will already be populated with property values.
	 * The returned bean instance may be a wrapper around the original.
	 * 
In case of a FactoryBean, this callback will be invoked for both the FactoryBean
	 * instance and the objects created by the FactoryBean (as of Spring 2.0). The
	 * post-processor can decide whether to apply to either the FactoryBean or created
	 * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
	 * 
This callback will also be invoked after a short-circuiting triggered by a
	 * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
	 * in contrast to all other BeanPostProcessor callbacks.
	 * 
The default implementation returns the given {@code bean} as-is.
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if {@code null}, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 * @see org.springframework.beans.factory.FactoryBean
	 */
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

}

我们先看一个BeanPostProcessor接口的实现类 ApplicationContextAwareProcessor 重点看这个类的实现方法，看源码我们知道，这个invokeAwareInterfaces方法做的事情， bean instanceof Aware 表示bean对象是不是Aware接口的实现类的实例对象。如果是 就会进行一系列的初始化操作。给属性赋值。

	@Override
	@Nullable
	public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
		AccessControlContext acc = null;

		if (System.getSecurityManager() != null &&
				(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
						bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
						bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
			acc = this.applicationContext.getBeanFactory().getAccessControlContext();
		}

		if (acc != null) {
			AccessController.doPrivileged((PrivilegedAction