核心监听器（启动工程时创建IOC）

1. 在web.xml中

   <!-- 指定spring核心配置文件路径 -->
   <context-param>
       <param-name>contextConfigLocation</param-name>
       <param-value>classpath:applicationContext.xml</param-value>
   </context-param>
   <!-- 配置监听器，当工程启动时，创建ioc容器，存放在ServletContext中 -->
   <listener>
       <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
   </listener>
   

   2.servlet获取IOC

   //从ServletContext中获取唯一的IOC容器
       ApplicationContext ac = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
       //从IOC容器中获取AccountService
       AccountService accountService = (AccountService) ac.getBean("accountService");