Laravel is a popular PHP open source framework. Its startup process is similar to other frameworks and requires certain preparations. This article will introduce in detail the startup process of Laravel.

1. Entry file index.php

Laravel’s entry file is index.php, and all requests will enter the framework through this file. In index.php, we can see the following code segment:

/*
|--------------------------------------------------------------------------
|?Turn?On?The?Lights
|--------------------------------------------------------------------------
|
|?We?need?to?illuminate?PHP?development,?so?let?us?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?our?users.
|
*/

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

This comment explains the function of the code. You can also see that require_once introduces the bootstrap/app.php file, which is the startup of Laravel. document.

2. Startup file bootstrap/app.php

In the app.php file, we can mainly see the instantiation of three key classes: $app, $kernel, $router. Let’s introduce them one by one below.

1. $app

$app is an instance of the Illuminate\Foundation\Application class and is the core of the entire framework. It manages the container of the Laravel application and provides many Powerful functions, such as routing, request handling, events, cookies, sessions, exception handling, etc. Next, let’s take a look at how $app is initialized.

In the constructor of $app, it first inherits the Illuminate\Container\Container class and generates a container instance. In this container instance we can bind and inject the services we need.

Next, it will register all core container services of Laravel, such as routing, logs, views, etc.

Finally, it will load the Laravel configuration files, which are stored in the config directory, and put them into the properties of the $app instance.

2. $kernel

$kernel is an instance of the Illuminate\Contracts\Http\Kernel interface. It is the HTTP core of Laravel and is responsible for processing all HTTP requests. A bridge between requests and responses. The main function of $kernel is to call the requested middleware, pass the request to the router, and finally pass the response to the client.

After $app is instantiated, it will call the $app->make() method and then obtain the $kernel instance through container resolution. In this process, the container of $app will parse the $config['app']['middleware'] configuration and register the middleware, and then store the middleware in the instance of $kernel.

3. $router

$router is an instance of the Illuminate\Routing\Router class, which is Laravel's router and handles all route parsing and distribution. The main function of $router is to match the request with the corresponding operation, and store the route to be processed for the request in the properties of the request instance.

After $app is instantiated, it will use the corresponding configuration to generate a router instance and register it in the Laravel container through the instance method of the $app instance.

In addition, it should be mentioned that $app will bind the request instance and other related instances to the container for use by middleware, routing and controllers. After the container binding is completed, Laravel has completed the preparation work.

3. Scheduling Requests

In Laravel, the request scheduling process is as follows:

1. Initiate an HTTP request from the client.

2. The request first passes through Laravel's public/index.php file and is forwarded to the bootstrap/app.php file.

3. In the bootstrap/app.php file, Laravel generates instances of $app, $kernel, and $router, and binds the request instance to the container. Then $app will call the handle method of $kernel to process the request.

4. In the handle method of $kernel, Laravel parses and calls the registered middleware in sequence through the container, and then forwards the request to the router.

5. In the router, Laravel extracts the URI from the request and matches it against all routes defined in the router instance. If a matching route is found, Laravel passes control to the appropriate controller.

6. The controller is the main handler of the request. It calls the business logic code to process the request and finally returns the result to the client as a response.

7. If the router does not find a matching route, it will pass the request to the error handler.

8. In the error handler, Laravel will generate a corresponding response and return it to the client based on the error type and configuration.

The above is the complete process of a Laravel request. By having an in-depth understanding of Laravel's startup process and request scheduling process, we can better understand its internal architecture and working principles, and thus better use it to handle our business.

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