RequestHandler: Is my code clean?
Just a quick observation I have made here, and this is by no means a full review, but you have some dead code here:

if ($parts) {
    $this-&gt;controller = ucfirst(array_shift($parts)) . 'Controller';
    $this-&gt;action     = array_shift($parts);
    $this-&gt;params     = ($parts) ? $parts : null;
}


It will only enter the if-block if $parts is true, and when assigning to $this-&gt;params you check it again, but it can never be null.

Therefore you should just assign $this-&gt;params = $parts;

Overall the readability of the code looks fine to me.