JavaWeb——使用会话维持状态3

这次的例子是使用会话给上一个例子添加登陆功能

1、页面逻辑

首先是登陆页面，这里需要输入账号和密码，输入正确后将进入商品列表页面，输入错误将会提示账号或者密码错误

其次是商品列表和购物车页面，添加了注销的链接

2、JSP

登陆页面的JSP，,loginFailed若为true表示用户已经尝试登陆且登陆出错，若为false表示用户还没用尝试登陆

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>login application</title>
</head>
<body>
    <h2>Login</h2>
    You must log in to access the customer support site.<br /><br />
    <%
        if(((Boolean)request.getAttribute("loginFailed")))
        {
    %>
    <b>The username or password you entered are not correct. Please try
        again.</b><br /><br />
    <%
        }
    %>
    <form method="POST" action="<c:url value="/login" />">
        Username<br />
        <input type="text" name="username" /><br /><br />
        Password<br />
        <input type="password" name="password" /><br /><br />
        <input type="submit" value="Log In" />
    </form>
</body>
</html>

然后就是把这行代码加到商品列表和购物车页面

 <a href="<c:url value="/login?logout=false" />">Logout</a>

3、代码逻辑

先是简单的建立账号密码数据库

    private static final Map<String, String> userDatabase = new Hashtable<>();
    static {
        userDatabase.put("user1","password1");
        userDatabase.put("user2","password2");
        userDatabase.put("user3","password3");
        userDatabase.put("user4","password4");
    }

然后是doGet方法的逻辑，注销的链接是直接重定向到登陆页面的，所以登陆页面先是判断是否需要清空Session，然后通过username检测是否已经登陆过了，然后就是将loginFailed设为false并将请求转发给login.jsp

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        if(request.getParameter("logout") != null)
        {
            request.getSession().invalidate();
            response.sendRedirect("login");
            return;
        }else if(session.getAttribute("username" )!= null)
        {
            response.sendRedirect("shop");
            return;
        }

        request.setAttribute("loginFailed",false);
        request.getRequestDispatcher("/WEB-INF/jsp/view/login.jsp")
                .forward(request, response);
    }

doPost将在用户点击提交时被调用，同样首先通过username检测是否已经登陆过，如果没有登陆过将检查账号密码是否有问题，没有问题重定向到商品列表页面，如果有问题的话将会把loginFailed设为true并将请求转发给login.jsp

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        if(session.getAttribute("username" )!= null)
        {
            response.sendRedirect("shop");
            return;
        }

        String username = request.getParameter("username");
        String password = request.getParameter("password");
        if(username == null || password == null ||
                !LoginServlet.userDatabase.containsKey(username)||
                !password.equals(LoginServlet.userDatabase.get(username))){
            request.setAttribute("loginFailed",true);
            request.getRequestDispatcher("/WEB-INF/jsp/view/login.jsp")
                    .forward(request,response);
        } else {
          session.setAttribute("username", username);
          request.changeSessionId();
          response.sendRedirect("shop");
        }
    }