一、保存作用域

• page：页面级别，基本不用
• request：一次请求响应范围
• session：一次会话范围
• application：整个应用程序范围

1.保存作用域

1.page

2.request

客户端重定向模式(两次请求响应)，请求1设置的uname，请求2获取不到 服务器端转发（一次请求响应），请求1设置的uname，可以获取的到

@WebServlet("/demo01")
public class Demo01Servlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.向request保存作用域，保存数据
        request.setAttribute("uname","lina");
        //2.客户端重定向
        response.sendRedirect("demo02");
        //3.服务器端转发
        request.getRequestDispatcher("demo02");
    }
}

3.session

一次会话范围都有效

@WebServlet("/demo03")
public class Demo03Servlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.向session保存作用域，保存数据
        request.getSession().setAttribute("uname","lina");
        //2.客户端重定向
        response.sendRedirect("demo02");
        //3.服务器端转发
        request.getRequestDispatcher("demo02");
    }
}

4.application

@WebServlet("/demo04")
public class Demo04Servlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.向application保存作用域保存数据
        //ServletContext Servlet上下文
        ServletContext application = request.getServletContext();
        application.setAttribute("uname","lina");

    }
}

二、路径

1.相对路径

2.绝对路径