yii2打开sessionuse  yii\web\Session; $session = Yii::$app->session;// check if a session is already openif ($session->isActive) ...// open a session$session->open();// close a session$session->close();// destroys all data registered to a session.$session->destroy();设置session$session = Yii::$app->session;$session->set('user_id', '1234');//OR$session['user_id'] = '1234';//OR$_SESSION['user_id'] = '1234';读取session$session = Yii::$app->session;$user_id = $session->get('user_id');//OR$user_id = $session['user_id'];//OR$user_id = isset($_SESSION['user_id']) ? $_SESSION['user_id'] : null;销毁session$session = Yii::$app->session;$session->remove('user_id');//ORunset($session['user_id']);//ORunset($_SESSION['user_id']);数组session的读取与设置$session = Yii::$app->session;$session['user'] = [    'id' => 1,    'username' => 'yiiuser',];echo $session['user']['id'];echo $session['user']['username']; $session['user.id'] = 1;$session['user.username'] = 'yiiuser';