如何计算一个网页打开需要多久，php代码如下：

<?php     
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>';
}
}

//新建测试页面test.php

<?php
include('Class_File_Open_Time.php');
$t = new executeTime();
phpinfo();