protected WebApplicationContext initWebApplicationContext() {
  //這裡通過WebApplicationContextUtils工具類來獲取根web應用上下文，這個上下文就是之前提到的全域性應用根上下文，儲存在ServletContext中，這個根上下文將作為當前mvc servlet上下文的雙親上下文。
   WebApplicationContext rootContext =
         WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;

   if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
      if (wac instanceof ConfigurableWebApplicationContext) {
         ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
         if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
            // setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
               // the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
            configureAndRefreshWebApplicationContext(cwac);
}
      }
   }
if (wac == null) {
// No context instance was injected at construction time -> see if one
      // has been registered in the servlet context. If one exists, it is assumed
      // that the parent context (if any) has already been set and that the
      // user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
    //這裡真正建立需要與該Servlet相關聯的WebApplicationContext
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}

if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
      // support or the context injected at construction time had already been
      // refreshed -> trigger initial onRefresh manually here.
//這裡，ioc容器已經建立初始化完成，執行onRefresh(wac)進一步初始化MVC其他模組，後面說明
onRefresh(wac);
}

if (this.publishContext) {
    //這裡將當前建立的上下文儲存到ServletContext中，attrName 是與當前servlet名相關聯，保證唯一性
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
      if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
   }

return wac;
}