Yii2 自定义class、自定义全局函数

1、在app\components下新建MyComponent.php

namespace app\components;

use Yii;
use yii\base\Component;
use yii\base\InvalidConfigException;

class MyComponent extends Component
{
 public function welcome()
 {
  echo "Hello..Welcome to MyComponent";
 }

}

2、在config/web.php加入你的components

'components' => [

         'mycomponent' => [

            'class' => 'app\components\MyComponent',

            ],
           ]

3、在controllers/TestController.php中用你的components

namespace app\controllers;
use Yii;

class TestController extends \yii\web\Controller
{
    public function actionWelcome()
    {
       Yii::$app->mycomponent->welcome();
    }

}