后台out.println向jsp页面推送中文时乱码

项目中有个判断session是否有效的功能，若session失效时，当用户点击其他需要访问到后台的链接时，则会alert出session失效的提示语句。然而在刷新列表时，用到了window.location.reload()这句代码，弹出的中文提示则变成乱码，其他情况下提示则正常。

原先代码如下：

public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
	     // TODO Auto-generated method stub  
        HttpServletRequest request = (HttpServletRequest) req;  
        HttpServletResponse response = (HttpServletResponse) resp;  
        HttpSession session = request.getSession();  
        String url = request.getServletPath();
        //这里判断目录，后缀名，当然也可以写在web.xml中，用url-pattern进行拦截映射  
        if ((!request.getServletPath().equals("/login.do"))) {  
            if (session.getAttribute("userSession") == null) {  
                session.invalidate();   //清空所有已定义的session
                response.setContentType("text/html;charset=gb2313");
                PrintWriter out = response.getWriter();                
                out.println("<script language='javascript' type='text/javascript'>");  
                out.println("alert('由于长时间没操作或者账号在其他地方登录，请重新登录!');");  
//                out.println("window.location.href='" + request.getContextPath() + "/index.jsp';");  
                out.println("</script>");  
            } else {  
                chain.doFilter(request, response);  
            }  
        } else {  
            chain.doFilter(request, response);  
        }  
	}

                response.setContentType("text/html;charset=gb2313");

                response.setContentType("text/html;charset=UTF-8");