折腾了2个小时，NND
ActionContext context = ActionContext.getContext();
HttpServletResponse response = (HttpServletResponse)context.get(ServletActionContext.HTTP_RESPONSE);
response.setCharacterEncoding("UTF-8");
...
response.getWriter().print("{success:false,msg:'请正确输入密码'}");
return null;//NND主要就是这里
一直在纠结return INPUT; -.-!!!
