A simple example Drupal Controller with an uncached JsonResponse

JsonController.php

<?php

namespace Drupal\example\Controller;

use Drupal\Core\Controller\ControllerBase;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\JsonResponse;

class ExampleController extends ControllerBase {
  public function getJson(Request $request) {
    $data = [];
    // Do some useful stuff to build an array of data.        

    return new JsonResponse($data);
  }
}