Codeigniter and Composer psr-4

Hi guys
composer.json

Code:

{
 "autoload": {
   "psr-4": {
     "App\\": "application/libraries"
   }
 }
}

application/libraries

PHP Code:

<?php
namespace App\Libraries;

class Welcome_library {

    public function __construct()
    {
        echo 'hi';
    }
} 


application/controllers

PHP Code:

<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Welcome extends CI_Controller {

    /**
     * Index Page for this controller.
     *
     * Maps to the following URL
     *        http://example.com/index.php/welcome
     *    - or -
     *        http://example.com/index.php/welcome/index
     *    - or -
     * Since this controller is set as the default controller in
     * config/routes.php, it's displayed at http://example.com/
     *
     * So any other public methods not prefixed with an underscore will
     * map to /index.php/welcome/<method_name>
     * @see https://codeigniter.com/user_guide/general/urls.html
     */
    public function index()
    {
        new App\Libraries\Welcome_library;
        $this->load->view('welcome_message');
    }
} 


PHP Code:

Fatal error: Class 'App\Libraries\Welcome_library' not found 


What am I doing wrong.
Thanks