core/app/Http/Controllers/Admin/UploadFile.php

<?php
namespace App\Http\Controllers\Admin;

use App\Http\Requests\UploadFileRequest;
use App\Models\File;
use Symfony\Component\HttpFoundation\File\Exception\FileException;

class UploadFile extends Controller
{
    /**
     * @var File
     */
    private $file;

    function __construct(File $file)
    {
        parent::__construct();
        $this->file = $file;
    }


    /**
     * Uploads any file
     *
     * @param UploadFileRequest $request
     *
     * @return \Illuminate\Http\RedirectResponse
     */
    public function postFile(UploadFileRequest $request)
    {
        if (!$request->hasFile('file')) {
            return $this->invalidUpload('noFileSpecified');
        }

        try {
            $uploadedFile = $this->file->upload($request->file('file'), $request);

            // we do not want to redirect
            if ($request->ajax()) {
                return $this->jsonResponse($uploadedFile);
            }

            // upload was not performed via ajax, redirect user
            return redirect()
                ->route('upload.overview', ['directory' => $request->directoryId])
                ->with('success', trans('admin/fileManager.uploadSuccessfull'));
        } catch (FileException $e) {
            return $this->invalidUpload('invalidFile');
        }
    }

    protected function invalidUpload($message)
    {
        return redirect()
            ->route('upload.file')
            ->with('error', trans('admin/fileManager.' . $message));
    }

    /**
     * Send response about uploaded file as JSON
     *
     * @param $uploadedFile
     *
     * @return \Illuminate\Http\JsonResponse
     */
    private function jsonResponse($uploadedFile)
    {
        $filename = $uploadedFile['file']->getFilename();
        $url = config('app.upload_path') . DIRECTORY_SEPARATOR . $filename;

        $data = [
            'filename' => $filename,
            'url'      => $url,
            'id'       => $uploadedFile['id']
        ];

        return response()->json($data);
    }
}