URL重写技术
数据保存在浏览器显示的页面中
<a href="xxxxx?userName=XX&&passWord=XX">跳到下一链接</a>
点击链接时，浏览器在跳转页面的同时，还会将?后的参数提交给后台
写：out的时候输入源代码
读：String value = request.getParameter("name");

例子代码如下：

protected void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        String userName = req.getParameter("userName");
        String passWord = req.getParameter("passWord");
        System.out.println(userName+"   "+passWord);
        res.setContentType("text/html;charset=UTF-8");
        PrintWriter out = res.getWriter();
        String url = "urlServlet?userName=aa&passWord=bb";
        out.println("<a href='"+url+"'>下一个</a>");
    }