Session operations after user login (setting of expiration time)

Users enter their username and password to log in. If it is empty, the database is not found or the password is wrong, return and log in again.

After successful login, it will be displayed:

Set the session expiration time and jump to:

If the user is already logged in, jump to:

The code is as follows:

success.php

<?php
/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2018/2/27 0027
 * Time: 上午 10:47
 */
header('Content-type:text/html;charset=utf-8');
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    if (empty($_POST['username'])){
        echo "<script>alert('用户名不能为空！');location.href='login.html';</script>";
    }else {
        $username=trim($_POST['username']);
    }
    if (empty($_POST['password'])){
        echo "<script>alert('密码不能为空！');location.href='login.html';</script>";
    }else{
        $password=$_POST['password'];
    }
}
$mysqli = new mysqli('localhost', 'root', 'root', 'student');
$result = $mysqli->query("SELECT password FROM user WHERE username = "."'$username'");
$rs=$result->fetch_row();
if (!empty($rs)){
    if ($password != $rs[0]) {
        echo "<script>alert('密码错误！');location.href='login.html';</script>";
    }else{
        $expire=3600;
        ini_set('session.gc_maxlifetime', $expire);//保存1小时
        if (empty($_COOKIE['PHPSESSID'])) {
            session_set_cookie_params($expire);
            session_start();
        }else{
            session_start();
            setcookie('PHPSESSID', session_id(), time() + $expire);
        }
        if(isset($_SESSION['username'])){
            exit("您已经登入了，请不要重新登入！用户名：{$_SESSION['username']}---<a href='logout.php'>注销</a>");
        }else{
            $_SESSION['username']=$_POST['username'];
        }
        echo "<script>alert('登录成功！');</script><br>";
        echo "您好！{$_SESSION['username']},欢迎回来！";
        echo "<a href='logout.php'>注销</a>";
    }
}else{
    echo "<script>alert('没有此用户！');location.href='login.html';</script>";
}