会话对象记录登录状态

2020-08-20

完成以下功能：

登录
登录成功后将此“已登录”状态保存
实现“显示员工列表”功能
当用户点击“显示员工列表”的时候，验证用户是否已登录，已登录则继续显示员工列表，没有登录则跳转到登录页面。
退出系统【把session对象销毁】

drop table if exists t_user;
create table t_user(
    id int(10) primary key auto_increment,
    username varchar(32) not null unique,
    password varchar(32) not null,
);

insert into t_user(username,password) values ("admin","123");

commit;
select * from t_user;

<!--login.html-->
<html>
    <head>
        <title>登录页面</title>
        <meta http-equiv = "keywords" content = "keyword1, keyword2, keyword3">
        <meta http-equiv = "description" content = "this is my page">
        <meta http-equiv = "content-type" content = "text/html;charset = UTF-8">
    </head>
    <body>
        <form action = "/hq/login" method = "post">
            用户名
                <input type = "text" name = "username">
                <br>
            密码
                <input type = "password" name = "password">
                <br>
            <input type = "checkbox" name = "tenDayAutoLoginFlag" value = "ok">十天内免登录<br>
            
            <input type = "submit" value = "登录">
        </form>
    </body>
</html>

<!--login-error.html-->
<html>
    <head>
        <title>登录失败</title>
        <meta http-equiv = "keywords" content = "keyword1, keyword2, keyword3">
        <meta http-equiv = "description" content = "this is my page">
        <meta http-equiv = "content-type" content = "text/html;charset = UTF-8">
    </head>
    <body>
        登录失败，请<a href = "/hq/login.html">重新登录</a>
    </body>
</html>

<!--index.html-->
<html>
    <head>
        <title>显示列表</title>
        <meta http-equiv = "keywords" content = "keyword1, keyword2, keyword3">
        <meta http-equiv = "description" content = "this is my page">
        <meta http-equiv = "content-type" content = "text/html;charset = UTF-8">
    </head>
    <body>
        <a href = "/hq/listEmp">显示员工列表</a>
    </body>
</html>

<!--web.xml-->
<welcome-file-list>
    <welcome-file>login.html</welcome-file>
</welcome-file-list>

<servlet>
    <servlet-name>login</servlet-name>
    <!--Servlet全类名-->
    <servlet-class>包名.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>login</servlet-name>
    <!--请求路径-->
    <url-pattern>/login</url-pattern>
</servlet-mapping>

<servlet>
    <servlet-name>listEmp</servlet-name>
    <!--Servlet全类名-->
    <servlet-class>包名.ListEmpServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>listEmp</servlet-name>
    <!--请求路径-->
    <url-pattern>/listEmp</url-pattern>
</servlet-mapping>

// LoginServlet.java
public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获取用户名和密码
        request.setCharacterEncoding("UTF-8");
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        // JDBC连接数据验证用户名和密码
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        User user = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "123");
            String sql = "select id,username,password from t_user where username=? and password=?";
            ps = conn.prepareStatement(sql);
            ps.setString(1, username);
            ps.setString(2, password);
            re = ps.executeQuery();
            if (rs.next()) {
                // 登录成功，用将用户信息包装到实体对象User中
                user = new User();
                user.setId(rs.getInt("id"));
                user.setUsername(rs.getString("username"));
                user.setPassword(rs.getString("password"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (rs != null) {
                try {
                    rs.close();
                } catch(SQLException e) {
                    e.printStackTrace();
                }
            }
            
            if (ps != null) {
                try {
                    ps.close();
                } catch(SQLException e) {
                    e.printStackTrace();
                }
            }
            
            if (conn != null) {
                try {
                    conn.close();
                } catch(SQLException e) {
                    e.printStackTrace();
                }
            }
        }
        
        
        if (user != null) {
            // 登录成功，将登陆成功的状态保存，跳转到index.html页面
            // 获取session对象
            HttpSession session = request.getSession();
            // 间登录成功用户存储到会话范围
            session.setAttribute("user", user);
            // 重定向
            response.sendRedirect(request.getContextPath + "/index.html");
            
        } else {
            // 登录失败跳转到失败页面
            response.sendRedirect(request.getContextPath + "/login-error.html");
        }
    }
}

// User.java
public class User {
    private int id;
    private String username;
    private String password;
    
    //getter&setter
    ......
}

// ListEmpServlet.java
public class ListEmpServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException      {
        // 验证用户是否已经登录
        // 已登录的标志是：session这个会话对象中保存了User
        HttpSession session = request.getSession(false);
        if (session != null && session.getAttribute("user") != null)   { 
            // 用户已登录，则查询员工列表并展示
            response.setContentType("text/html;charset=UTF-8");
            PrintWriter out = response.getWriter();
            // 从数据库获取员工列表
            Connection conn = null;
            PreparedStatement ps = null;
            ResultSet rs = null;
            try {
                Class.forName("com.mysql.jdbc.Driver");
                conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "123");
                String sql = "select empno,ename,sal,hiredate from emp order by sal asc";
                ps = conn.prepareStatement(sql)
                re = ps.executeQuery();
                if (rs.next()) {
                    String empno = rs.getString("empno");
                    String ename = rs.getString("ename");
                    String sal = rs.getString("sal");
                    String hiredate = rs.getString("hiredate");

                }
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (rs != null) {
                    try {
                        rs.close();
                    } catch(SQLException e) {
                        e.printStackTrace();
                    }
                }

                if (ps != null) {
                    try {
                        ps.close();
                    } catch(SQLException e) {
                        e.printStackTrace();
                    }
                }

                if (conn != null) {
                    try {
                        conn.close();
                    } catch(SQLException e) {
                        e.printStackTrace();
                    }
                }
            }
        
            // 展示员工列表
            out.print.......    
        } else {
            // 用户未登录跳转到登录页面
            response.sendRedirect(request.getContextPath + "/login.html");
        } 
        
        
    }
}