Detailed explanation of Laravel's life cycle

The following is the tutorial column of Laravel to introduce you to the life cycle of Laravel. I hope it will be helpful to friends in need!

Laravel’s life cycle

Everything in the world has a life cycle, and we need to understand it when we use any tool It works, then it will be easy to use, and the same is true for application development. Once you understand its principles, you will be able to use it with ease.
Before understanding the life cycle of Laravel, let us first review the life cycle of PHP.

Life cycle of PHP

Operation mode of PHP

The two operating modes of PHP are WEB mode, CLI mode.

1. When we type the php command in the terminal, we are using the CLI mode.
2. When using Nginx or another web server as the host to process an incoming request, the WEB mode is used.

Life cycle

When we request a php file, PHP will undergo 5 stages in order to complete the request. Life cycle switching:

1. Module initialization (MINIT), that is, calling the extended initialization function specified in php.ini to perform initialization work, such as mysql Extension.

2. Request initialization (RINIT), that is, initialize the symbol table with variable names and variable value contents required to execute this script, such as $_SESSION variables.

3. Execute the PHP script.

4. After the request processing is completed (Request Shutdown), call the RSHUTDOWN method of each module in sequence, and call the unset function for each variable, such as unset $_SESSION variable.

5. Closing the module (Module Shutdown), PHP calls the MSHUTDOWN method of each extension. This is the last opportunity for each module to release memory. This means there is no next request.

WEB mode is very similar to CLI (command line) mode. The difference is:

1. CLI mode will go through a complete 5 cycles each time the script is executed. , because there will be no next request after your script is executed;
2. WEB mode may use multi-threading to cope with concurrency, so life cycles 1 and 5 are possible It is only executed once, and the life cycle of 2-4 is repeated when the next request comes, thus saving the overhead caused by system module initialization.

It can be seen that the PHP life cycle is very symmetrical. Having said all this, it is just to locate where Laravel is running. Yes, Laravel only runs in the third stage:

PHP life cycle

Function

Understand these, you can optimize your Laravel code, and have a deeper understanding of Laravel's singleton (single case ). At least you know that at the end of each request, PHP's variables will be unset, and Laravel's singleton is only singleton during a certain request; you are in Laravel Static variables in cannot be shared between multiple requests, because each request will be unset at the end. Understanding these concepts is the first and most critical step to writing high-quality code. So remember, PHP is a scripting language, and all variables will only take effect in this request and will be reset on the next request, unlike Java static variables that have global effects.

Laravel’s life cycle

Overview

Laravel’s life cycle starts from public\index.phpStart and end with public\index.php.

Request process

The following is the full source code of public\index.php, which can be divided into Four steps:

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

2. $app = require_once __DIR__.'/../bootstrap/app.php';
   $kernel = $app->make(Illuminate\Contracts\Http\Kernel::class);

3. $response = $kernel->handle(
      $request = Illuminate\Http\Request::capture()
   );
   $response->send();

4. $kernel->terminate($request, $response);

The following is a detailed explanation of the four steps:
composer automatically loads the required classes

1. The file loads the auto-loading settings generated by composer, Include all your composer require dependencies.

2. Generate container Container, Application instance, and register core components (HttpKernel, ConsoleKernel, ExceptionHandler) with the container (corresponding to code 2, the container is very important, and will be explained in detail later).

3. Process the request, generate and send the response (corresponding to code 3, it is no exaggeration to say that 99% of your code runs in this small handle method).

4. 请求结束，进行回调（对应代码4，还记得可终止中间件吗？没错，就是在这里回调的）。

Laravel 的请求步骤

我们不妨在详细一点：

第一步：注册加载composer自动生成的class loader

就是加载初始化第三方依赖。

第二步：生成容器 Container

并向容器注册核心组件，是从 bootstrap/app.php 脚本获取 Laravel 应用实例，

第三步：这一步是重点，处理请求，并生成发送响应。

请求被发送到 HTTP 内核或 Console 内核，这取决于进入应用的请求类型。

取决于是通过浏览器请求还是通过控制台请求。这里我们主要是通过浏览器请求。

HTTP 内核继承自 Illuminate\Foundation\Http\Kernel 类，该类定义了一个 bootstrappers 数组，这个数组中的类在请求被执行前运行，这些 bootstrappers 配置了错误处理、日志、检测应用环境以及其它在请求被处理前需要执行的任务。

protected $bootstrappers = [
        //注册系统环境配置 （.env）
        'Illuminate\Foundation\Bootstrap\DetectEnvironment',
        //注册系统配置（config）
        'Illuminate\Foundation\Bootstrap\LoadConfiguration',
        //注册日志配置
        'Illuminate\Foundation\Bootstrap\ConfigureLogging',
        //注册异常处理
        'Illuminate\Foundation\Bootstrap\HandleExceptions',
        //注册服务容器的门面，Facade 是个提供从容器访问对象的类。
        'Illuminate\Foundation\Bootstrap\RegisterFacades',
        //注册服务提供者
        'Illuminate\Foundation\Bootstrap\RegisterProviders',
        //注册服务提供者 `boot`
        'Illuminate\Foundation\Bootstrap\BootProviders',
    ];

注意顺序：
Facades 先于ServiceProviders，Facades也是重点，后面说，这里简单提一下，注册 Facades 就是注册 config\app.php中的aliases 数组，你使用的很多类，如Auth，Cache,DB等等都是Facades；而ServiceProviders的register方法永远先于boot方法执行，以免产生boot方法依赖某个实例而该实例还未注册的现象。

HTTP 内核还定义了一系列所有请求在处理前需要经过的 HTTP 中间件，这些中间件处理 HTTP 会话的读写、判断应用是否处于维护模式、验证 CSRF 令牌等等。

HTTP 内核的标志性方法 handle处理的逻辑相当简单：获取一个 Request，返回一个 Response，把该内核想象作一个代表整个应用的大黑盒子，输入 HTTP 请求，返回 HTTP 响应。

第四步：将请求传递给路由。

在Laravel基础的服务启动之后，就要把请求传递给路由了。路由器将会分发请求到路由或控制器，同时运行所有路由指定的中间件。

传递给路由是通过 Pipeline（管道）来传递的，但是Pipeline有一堵墙，在传递给路由之前所有请求都要经过，这堵墙定义在app\Http\Kernel.php中的$middleware数组中，没错就是中间件，默认只有一个CheckForMaintenanceMode中间件，用来检测你的网站是否暂时关闭。这是一个全局中间件，所有请求都要经过，你也可以添加自己的全局中间件。

然后遍历所有注册的路由，找到最先符合的第一个路由，经过它的路由中间件，进入到控制器或者闭包函数，执行你的具体逻辑代码。

所以，当请求到达你写的代码之前，Laravel已经做了大量工作，请求也经过了千难万险，那些不符合或者恶意的的请求已被Laravel隔离在外。

Detailed explanation of Laravels life cycle

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