主要流程
1.创建BeanFactory. BeanDefinition注册到BeanFactory中beanDefinitionMap属性中.
2.实例化 & 执行所有BeanFactoryPostProcessor#postProcessBeanFactory
3.实例化 & 注册所有BeanPostProcessor接口的实现类
for () {
4.执行所有InstantiationAwareBeanPostProcessorAdapter#postProcessBeforeInstantiation
5.实例化bean
6.执行所有InstantiationAwareBeanPostProcessorAdapter#postProcessAfterInstantiation
7.执行所有BeanPostProcessor#postProcessBeforeInitialization
8.初始化bean
9.执行所有BeanPostProcessor#postProcessAfterInitialization
}