How to catch Joomla\CMS\Router\Exception\RouteNotFoundException in Joomla 4.1?

Question

As per the title, how can we catch a RouteNotFoundException? For time constraints, instead of creating a custom component we opted for some hand-waving, and decided to display custom content at non-routed URL's, and it's working, but we would like to catch the exception. I tried acting on error.php and index.php, but to no avail.

Answer 1

In J4 exceptions can be handled by system plugins with onError event:

use Joomla\CMS\Event\ErrorEvent;
use Joomla\CMS\Plugin\CMSPlugin;
use Joomla\CMS\Router\Exception\RouteNotFoundException;

class PlgSystemExample extends CMSPlugin
{
    public function onError(ErrorEvent $event)
    {
        if ($event->getError() instanceof RouteNotFoundException)
        {
            // Handle the exception.
        }
    }
}