Introduction
When using any tool in the "real world", you feel more confident if you understand how that tool works. Application development is no different. When you understand how your development tools function, you feel more comfortable and confident using them.
The goal of this document is to give you a good, high-level overview of how the Laravel framework works. By getting to know the overall framework better, everything feels less "magical" and you will be more confident building your applications. If you don't understand all of the terms right away, don't lose heart! Just try to get a basic grasp of what is going on, and your knowledge will grow as you explore other sections of the documentation.
Lifecycle Overview
First Things
The entry point for all requests to a Laravel application is the
public/index.php file. All requests are directed to this
file by your web server (Apache / Nginx) configuration. The
index.php file doesn't contain much code. Rather, it is a
starting point for loading the rest of the framework.
The index.php file loads the Composer generated
autoloader definition, and then retrieves an instance of the Laravel
application from bootstrap/app.php script. The first action
taken by Laravel itself is to create an instance of the application / service container.
HTTP / Console Kernels
Next, the incoming request is sent to either the HTTP kernel or the
console kernel, depending on the type of request that is entering the
application. These two kernels serve as the central location that all
requests flow through. For now, let's just focus on the HTTP kernel,
which is located in app/Http/Kernel.php.
The HTTP kernel extends the
Illuminate\Foundation\Http\Kernel class, which defines an
array of bootstrappers that will be run before the request
is executed. These bootstrappers configure error handling, configure
logging, detect
the application environment, and perform other tasks that need to be
done before the request is actually handled.
The HTTP kernel also defines a list of HTTP middleware that all requests must pass through before being handled by the application. These middleware handle reading and writing the HTTP session, determining if the application is in maintenance mode, verifying the CSRF token, and more.
The method signature for the HTTP kernel's handle method
is quite simple: receive a Request and return a
Response. Think of the Kernel as being a big black box that
represents your entire application. Feed it HTTP requests and it will
return HTTP responses.
Service Providers
One of the most important Kernel bootstrapping actions is loading the
service providers for your application. All
of the service providers for the application are configured in the
config/app.php configuration file's providers
array. First, the register method will be called on all
providers, then, once all providers have been registered, the
boot method will be called.
Service providers are responsible for bootstrapping all of the framework's various components, such as the database, queue, validation, and routing components. Since they bootstrap and configure every feature offered by the framework, service providers are the most important aspect of the entire Laravel bootstrap process.
Dispatch Request
Once the application has been bootstrapped and all service providers
have been registered, the Request will be handed off to the
router for dispatching. The router will dispatch the request to a route
or controller, as well as run any route specific middleware.
Focus On Service Providers
Service providers are truly the key to bootstrapping a Laravel application. The application instance is created, the service providers are registered, and the request is handed to the bootstrapped application. It's really that simple!
Having a firm grasp of how a Laravel application is built and
bootstrapped via service providers is very valuable. Of course, your
application's default service providers are stored in the
app/Providers directory.
By default, the AppServiceProvider is fairly empty. This
provider is a great place to add your application's own bootstrapping
and service container bindings. Of course, for large applications, you
may wish to create several service providers, each with a more granular
type of bootstrapping.