如何在web环境中配置applicationContext.xml文件?

<listener>
  <listener-class>
   org.springframework.web.context.ContextLoaderListener
  </listener-class>
 </listener>
 或：
 <servlet>
  <servlet-name>context</servlet-name>
   <servlet-class>
    org.springframework.web.context.ContextLoaderServlet
   </servlet-class>
  <load-on-startup>1</load-on-startup>
 </servlet>
 通过如下方法取出applicationContext实例:
 ApplicationContext ac=WebApplicationContextUtils.getWebApplicationContext(this.getServletContext);