How to check database exception before Application Launch

Hi,
I've completed developing a Restful API with CI4. 
Just wondering how can we throw a custom message when the database connection cannot be created, or when it's temporarily lost?

Currently, there is no suitable tool for assigning custom handlers.
But there are several options.
1. You can create file app/Views/errors/html/error_8.php
8 - EXIT_DATABASE constant.
This file will be used as a template for the DatabaseException.

2. You can create your own exception handler class by extending CodeIgniter\Debug\Exceptions::class.
And overriding the Services::exceptions() factory.

I see.. let me give a try. thanks @iRedds

1. You can create file app/Views/errors/html/error_8.php
8 - EXIT_DATABASE constant.
This file will be used as a template for the DatabaseException.

This is a bug, and it will not work in v4.3.
See https://github.com/codeigniter4/CodeIgniter4/pull/6228

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@kenjis Why did you need to make a bug? =)
So the only error pattern now is 404?

8 is not a HTTP status code. The error_*.php is for the HTTP status code.

ci-phpunit-test | CodeIgniter Testing Guide | CodeIgniter 3 to 4 Upgrade Helper

It feels like we shot ourselves in the foot with this PR.
Now the only way to handle exceptions custom is to modify CodeIgniter\Debug\Exceptions::class.