Custom Class not loading in Controller

I have a file called InvoiceDataSource.php and it's path is app\Core\Forms\Invoice\InvoiceDataSource.php, and that file contains this.

<?php

namespace App\Core\Forms\Invoice;

class InvoiceDataSource {

public function getAllCustomers(){

    return Customer::selectRaw('id as `value`,'.
                     'name as `label`')
                    ->get()
                    ->toArray();
}

}

?>

I have included this in composer.json file as well like so,

"autoload": {
    "classmap": [
        "database/seeds",
        "database/factories",
        "app/Core/Forms/Invoice/InvoiceDataSource.php" 
    ],
    "psr-4": {
        "App\\": "app/"
    }
},

It has also been added to autoloader in autoload_classmap.php file.

Now when I am trying to access this in the controller like this

//
public function getDataSource($id,Request $request){

    return InvoiceDataSource::getAllCustomers();

}

But for some reason the error read this,

{message: "Class 'App\Http\Controllers\InvoiceDataSource' not found",…}
exception: "Symfony\Component\Debug\Exception\FatalThrowableError"
file: "/home/zrehan/projects/erp/app/Http/Controllers/FormController.php"
line: 88
message: "Class 'App\Http\Controllers\InvoiceDataSource' not found"
trace: [{function: "getDataSource", class: "App\Http\Controllers\FormController", type: "->"},…]

Can someone help me with this?

via Chebli Mohamed