最大的 应用域对象 ServletContext

中间的 会话域对象 HttpSession

最小的 请求域对象 HttpServletRequest

域对象的API

API测试

• ServletA向三大域中放入数据

@WebServlet("/servletA")
public class ServletA extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 向请求域中放入数据
        req.setAttribute("request","request-message");
        //req.getRequestDispatcher("servletB").forward(req,resp);
        // 向会话域中放入数据
        HttpSession session = req.getSession();
        session.setAttribute("session","session-message");
        // 向应用域中放入数据
        ServletContext application = getServletContext();
        application.setAttribute("application","application-message");

    }
}

• ServletB从三大于中取出数据

@WebServlet("/servletB")
public class ServletB extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 从请求域中获取数据
        String reqMessage =(String)req.getAttribute("request");
        System.out.println(reqMessage);

        // 从会话域中获取数据
        HttpSession session = req.getSession();
        String sessionMessage =(String)session.getAttribute("session");
        System.out.println(sessionMessage);
        // 从应用域中获取数据
        ServletContext application = getServletContext();
        String applicationMessage =(String)application.getAttribute("application");
        System.out.println(applicationMessage);
    }
}