myblog/Application/Admin/Controller/BaseController.class.php

<?php
namespace Admin\Controller;
use Think\Controller;
class BaseController extends Controller {
    public function _initialize(){
		if (isset($_SESSION['user_name'])) {
			//已登陆，不做任何操作
		}else{
			//  $this->redirect('Login/login');
			$this->error('非法操作！',U('Login/login'));
		}
    }
}