Struts2的Action中取得request，response，session等对象的方法

方法如下：

HttpServletRequest request =(HttpServletRequest)ActionContext.getContext().get(ServletActionContext.HTTP_REQUEST);       
      
HttpServletResponse response =HttpServletResponse)ActionContext.getContext().get(ServletActionContext.HTTP_RESPONSE);       
       
//ServletActionContext.APPLICATION;       
//ServletActionContext.SESSION;       
//ServletActionContext.PAGE_CONTEXT;