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 simply 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, determine 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.
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.