spring有2个容器，一个放controller（位于child），一个放组件（位于parent）
| child | WebApplicationContext webApp=RequestContextUtils.getWebApplicationContext(request , request.getSession().getServletContext()); |
| parent | ApplicationContext ac1 = WebApplicationContextUtils.getRequiredWebApplicationContext(request.getSession().getServletContext()); |
| parent | ApplicationContext ac2 = WebApplicationContextUtils.getWebApplicationContext(request.getSession().getServletContext()); |
| parent | WebApplicationContext webApplicationContext = (WebApplicationContext) request.getSession().getServletContext().getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE); |
| parent | WebApplicationContext cc = ContextLoader.getCurrentWebApplicationContext() |