PHP 计算页面执行时间

<?php
$t = new executeTime;
 
phpinfo();
 
class executeTime{
    private $microtime;
    public function __construct(){
        $this->microtime = microtime(true);
    }
 
        public function getNow(){
                $this->__dectruct();
        }
 
    public function __destruct(){
        if (empty($_SERVER['REQUEST_TIME_FLOAT']))
            echo '<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次执行时间：', microtime(TRUE) - $this->microtime, '秒</div>';
        else
            echo '<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次执行时间：', microtime(TRUE) - $_SERVER['REQUEST_TIME_FLOAT'], '秒</div>';
    }
}