thinkphp 5框架实现登陆，登出及session登陆状态检测功能示例

?php
namespace app\Admin\controller;
use think\Controller;
use think\Session;
class Basic extends Controller
{
  //如果你的控制器类继承了\think\Controller类的话，可以定义控制器初始化方法_initialize，在该控制器的方法调用之前首先执行。
  public function _initialize()
  {
    //判断有无admin_username这个session，如果没有，跳转到登陆界面
    if(!session('admin_username')){
      return $this->error('您没有登陆',url('Login/login'));
    }
  }
}

!DOCTYPE html>
html lang="en">
head>
  meta charset="UTF-8">
  meta name="viewport" content="width=device-width, initial-scale=1.0">
  meta http-equiv="X-UA-Compatible" content="ie=edge">
  title>Document/title>
/head>
body>
  h1>登陆/h1>
  div>
    form class="m-t" role="form" action="{url('Login/login')}" method="post">
      div class="input-field">
        input id="admin_username" type="text" name="admin_username" class=" validate" placeholder="请输入用户名" required>
        label for="admin_username">用户名/label>
      /div>
      div class="input-field">
        input id="admin_password" type="password" name="admin_password" placeholder="请输入密码" class="validate" required>
        label for="admin_password">密码/label>
      /div>
      button type="submit" class="waves-effect red lighten-1 waves-light btn full-width " style="margin-top:10px; height:40px;">登 录/button>
    /form>
  /div>
/body>
/html>

?php
namespace app\Admin\controller;
use think\Controller;
use think\Session;
use think\Request;
use think\Db;
class Login extends Controller{
  public function login(){
//判断是否是post方法发送的数据：如果是则开始登陆
    if (Request::instance()->isPost()){
      $admin_username = input('post.admin_username');//接收前台用户名
      $admin_password = input('post.admin_password');//接收前台密码
      if(empty($admin_username) || empty($admin_password)){
        $this->error("用户名或者密码不能为空！");
      }
      //从数据库读取数据
      $admin_info = DB::name('admin')
      ->where('admin_username',$admin_username)
      ->find();
      if(empty($admin_info)){
        $this->error('用户不存在，请重新登陆',url('Login/login'));
      }else{
        if(md5($admin_password)!=$admin_info['admin_password']){
          $this->error('密码不正确，请重新登陆',url('Login/login'));
        }else{
          Session::set('admin_username',$admin_username);
          $this->success("登录成功！",url('Index/index'));
        }
      }
    }else{//如果不是post，则返回登陆界面
      return view('login');
    }
  }
  public function logout(){
    session(null);//退出清空session
    return $this->success('退出成功',url('Login/login'));//跳转到登录页面
  }
}

?php
namespace app\Admin\controller;
use think\Controller;
use think\Session;
use think\View;
//后台首页继承自登陆判断页面，每次加载都会先执行判断页面的代码
class Index extends Basic
{
  public function index()
  {
    $view = new View();
    $data = session('admin_username');
    $view->assign('data',$data);
    //return view('index');
    return $view->fetch('index');
  }
}

!DOCTYPE html>
html lang="en">
head>
  meta charset="UTF-8">
  meta name="viewport" content="width=device-width, initial-scale=1.0">
  meta http-equiv="X-UA-Compatible" content="ie=edge">
  title>Document/title>
/head>
body>
  !-- h1>hello,{$Think.session.admin_username}/h1> -->
  h1>hello,{$data}/h1>
  a href="{:url('Login/logout')}" rel="external nofollow" >退出登陆/a>
/body>
/html>