servlet如何将后台数据推送到前台

servlet如何将后台数据推送到前台

public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html")
PrintWriter out = response.getWriter()
out.println("   alert(修改成功)</script>")
out.println("")
out.flush()
out.close()
request.getRequestDispatcher("bill.jsp")
}

这是servlet的dopost（）方法，