Servlet中的三大域对象

共同的功能

存值/取值

getAttribute 存值
setAttribute 取值

1.request 请求域

使用范围：一次请求

@WebServlet("/as")
public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        

        /**在/as向request域中存值*/
        req.setAttribute("salary",10000);
       
    }
}

@WebServlet("/bs")
public class BServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       

        /**在bs中向request域中取值*/
        Object salary = req.getAttribute("salary");
        System.out.println(salary);

    }
}

2.session 会话域

使用范围：多次请求

@WebServlet("/cs")
public class CServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("====在cs中向session域存值====");
        req.getSession().setAttribute("salary",1000000);

    }
}

@WebServlet("/ds")
public class DServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("====在ds中从session域取值====");
        Object salary = req.getSession().getAttribute("salary");
        System.out.println(salary);
    }
}

3.application 全局域

使用范围：与服务器相同寿命

@WebServlet("/es")
public class EServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("====在es中向application域存值====");
        req.getSession().getServletContext().setAttribute("salary",123456);
    }
}

@WebServlet("/fs")
public class FServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("====在fs中从application域中取值====");
        Object salary = req.getSession().getServletContext().getAttribute("salary");
        System.out.println(salary);
    }
}