- IoC
两个基础包：
org.springframework.beans 和 org.springframework.context
接口：
BeanFactory：通过高级配置机制可以管理任何类型的对象
ApplicationContext：BeanFactory的子接口，特点是它更简单的整合spring AOP特性；消息资源处理(for use in internationalization)；Event publication；Application-layer specific contexts such as the WebApplicationContext for use in web applications.
In short, the BeanFactory provides the configuration framework and basic functionality, and the ApplicationContext adds more enterprise-specific functionality. The ApplicationContext is a complete superset of the BeanFactory.
The org.springframework.context.ApplicationContext interface represents the Spring IoC container and is responsible for instantiating, configuring, and assembling the beans.