session 生命周期和经典案例-防止非法进入管理页面

public class CreateSession2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("CreateSession2 被调用");
        //创建session
        HttpSession session = request.getSession();
        System.out.println("CreateSession2 sid= " + session.getId());
        //设置生命周期为 60s
        session.setMaxInactiveInterval(60);
        session.setAttribute("u", "jack");
        //回复一下浏览器
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("<h1>创建session成功, 设置生命周期60s</h1>");
        writer.flush();
        writer.close();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

public class ReadSession2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //System.out.println("ReadSession2 被调用...");
        //1. 获取到session
        HttpSession session = request.getSession();
        System.out.println("ReadSession2 sid= " + session.getId());
        //2. 读取session的属性
        Object u = session.getAttribute("u");
        if (u != null) {
            System.out.println("读取到session属性 u= " + (String) u);
        } else {
            System.out.println("读取不到session属性 u 说明原来的session被销毁");
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

public class DeleteSession extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("DeleteSession 被调用...");
        //演示如何删除session
        HttpSession session = request.getSession();
        session.invalidate();
        // 如果你要删除session的某个属性
        //session.removeAttribute("xxx");
        //回复一下浏览器
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("<h1>删除session成功</h1>");
        writer.flush();
        writer.close();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>登录页面</title>
</head>
<body>
<h1>用户登录界面</h1>
<form action="/cs/loginCheck" method="post">
    u:<input type="text" name="username"><br/>
    p:<input type="password" name="pwd"><br/>
    <input type="submit" value="登录">
</form>
</body>
</html>

public class LoginCheckServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("LoginCheckServlet 被调用..");
        //功能-> 自己拆解 -> 逐步实现
        //1. 得到提交的用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        if("666666".equals(password)) {//认为合法
            //把用户名保存到 session
            HttpSession session = request.getSession();
            session.setAttribute("loginuser", username);
            //请求转发到ManageServlet
            request.getRequestDispatcher("/manage").forward(request, response);
        } else {
            //请求转发进入到 error.html
            request.getRequestDispatcher("/error.html").forward(request, response);
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

public class ManageServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //判断该用户是否登录过
        HttpSession session = request.getSession();
        Object loginuser = session.getAttribute("loginuser");
        if(loginuser == null) {//说明该用户没有登录
            //重新登录-> 请求重定向
            //response.sendRedirect("/cs/userlogin.html");
            response.sendRedirect(request.getContextPath() + "/userlogin.html");
            return;
        } else {
            response.setContentType("text/html;charset=utf-8");
            PrintWriter writer = response.getWriter();
            writer.println("<h1>用户管理页面</h1>");
            writer.println("欢迎你, 管理员：" + loginuser.toString());
            writer.flush();
            writer.close();
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>登录失败</title>
</head>
<body>
<h1>登录失败</h1>
<!--
web工程路径专题
1. a 标签是 浏览器解析
2. 第一 / 被解析成 http://localhost:8080/
3. 如果没有 / 会以当前浏览器地址栏 的 http://localhost:8080/工程路径../资源 去掉资源部分作为参考路径
-->
<a href="/cs/userlogin.html">点击重新登录</a>
</body>
</html>