请求转发学习

（1）浏览器地址栏不会发生变化
（2）只有一次请求
（3）共享request域中的数据
（4）可以转发到web-Inf目录下（正常情况下是不发访问到该目录下的）
（5）无法访问工程以外的servlet
（5）只能转发给doget()方法

servlet1

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("servlet3");
        String name = request.getParameter("name");
        System.out.println("name:"+name);
        request.setAttribute("password",123);
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/servlet4");
        requestDispatcher.forward(request,response);
    }

servlet2

 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("servlet4");
        String name = request.getParameter("name");
        System.out.println("name:"+name);
        Object password = request.getAttribute("password");
        System.out.println(password);
    }

 RequestDispatcher requestDispatcher = 
 request.getRequestDispatcher("/servlet4");
 requestDispatcher.forward(request,response);