Laravel框架的入口檔案，所有PHP框架都有這樣一支檔案。
注意index.php檔不在根目錄，而是在public資料夾裏面。Apache調整路徑的.htaccess也在那兒。
因此，web server的根目錄不會設成Laravel的根目錄，而是public資料夾。
這麼做是因為資安考量：public內通常還會放個assets資料夾(擺放css/js/img等檔案)之類的、只允許public資料夾被使用者接觸到、讓其他地方的檔案不會被惡意使用者碰到。
舉CodeIgniter2.1.4版本為反例：index.php放在根目錄，導致所有資料夾都有可能被使用者接觸到。結果只好在所有檔案前面加上：

然後在每個資料夾建立index.html檔：


	



Directory access is forbidden.




作為防禦了，挺煩的。

 */

/*
|--------------------------------------------------------------------------
| Register The Auto Loader
|--------------------------------------------------------------------------
|
| Composer provides a convenient, automatically generated class loader
| for our application. We just need to utilize it! We'll require it
| into the script here so that we do not have to worry about the
| loading of any our classes "manually". Feels great to relax.
|
*/

require __DIR__.'/../bootstrap/autoload.php';

載入一個會自動載入所需類別的php檔，讓開發人員不需要手動載入他們。

參見：自動載入類別：bootstrap/autoload.php
/*
|--------------------------------------------------------------------------
| Turn On The Lights
|--------------------------------------------------------------------------
|
| We need to illuminate PHP development, so let's turn on the lights.
| This bootstraps the framework and gets it ready for use, then it
| will load up this application so that we can run it and send
| the responses back to the browser and delight these users.
|
*/

$app = require_once __DIR__.'/../bootstrap/start.php';

載入框架本身。
/*
|--------------------------------------------------------------------------
| Run The Application
|--------------------------------------------------------------------------
|
| Once we have the application, we can simply call the run method,
| which will execute the request and send the response back to
| the client's browser allowing them to enjoy the creative
| and wonderful application we have whipped up for them.
|
*/

$app->run();

呼叫run函式，接收request、處理，最後送出相應的response回去。