如果你对一件工具的使用原理了如指掌，那么你在用这件工具的时候会充满信心！
一旦用户（浏览器）发送了一个HTTP请求，我们的apache或者nginx一般都转到index.php，因此，之后的一系列步骤都是从index.php开始的，我们先来看一看这个文件代码。
<?php
require __DIR__.'/../bootstrap/autoload.php';
$app = require_once __DIR__.'/../bootstrap/app.php';
/*
|--------------------------------------------------------------------------
| Run The Application
|--------------------------------------------------------------------------
|
| Once we have the application, we can handle the incoming request
| through the kernel, and send the associated response back to
| the client's browser allowing them to enjoy the creative
| and wonderful application we have prepared for them.
|
*/
$kernel = $app->make(IlluminateContractsHttpKernel::class);
$response = $kernel->handle(
$request = IlluminateHttpRequest::capture()
);
$response->send();
$kernel->terminate($request, $response);
作者在注释里谈了$kernel的作用，$kernel处理来访的请求，并且发送相应返回给用户浏览器。
这里又涉及到了一个$app对象，所以附上$app对象的源码，这份源码是ootstrapapp.php
<?php
/*
|--------------------------------------------------------------------------
| Create The Application
|--------------------------------------------------------------------------
|
| The first thing we will do is create a new Laravel application instance
| which serves as the "glue" for all the components of Laravel, and is
| the IoC container for the system binding all of the various parts.
|
*/
$app = new IlluminateFoundationApplication(
realpath(__DIR__.'/../')
);
/*
|--------------------------------------------------------------------------
| Bind Important Interfaces
|--------------------------------------------------------------------------
|
| Next, we need to bind some important interfaces into the container so
| we will be able to resolve them when needed. The kernels serve the
| incoming requests to this application from both the web and CLI.
|
*/
$app->singleton(
IlluminateContractsHttpKernel::class,
AppHttpKernel::class
);
$app->singleton(
IlluminateContractsConsoleKernel::class,
AppConsoleKernel::class
);
$app->singleton(
IlluminateContractsDebugExceptionHandler::class,
AppExceptionsHandler::class
);
/*
|--------------------------------------------------------------------------
| Return The Application
|--------------------------------------------------------------------------
|
| This script returns the application instance. The instance is given to
| the calling script so we can separate the building of the instances
| from the actual running of the application and sending responses.
|
*/
return $app;
请看app变量是IlluminateFoundationApplication类的对象，所以调用了这个类的构造函数，具体做了什么事，我们看源码。
public function __construct($basePath = null)
{
if ($basePath) {
$this->setBasePath($basePath);
}
$this->registerBaseBindings();
$this->registerBaseServiceProviders();
$this->registerCoreContainerAliases();
}
构造器做了3件事，前两件事很好理解，创建Container，注册了ServiceProvider，看代码
/**
* Register the basic bindings into the container.
*
* @return void
*/
protected function registerBaseBindings()
{
static::setInstance($this);
$this->instance('app', $this);
$this->instance(Container::class, $this);
}
/**
* Register all of the base service providers.
*
* @return void
*/
protected function registerBaseServiceProviders()
{
$this->register(new EventServiceProvider($this));
$this->register(new LogServiceProvider($this));
$this->register(new RoutingServiceProvider($this));
}
最后一件事，是做了个很大的数组，定义了大量的别名，侧面体现程序员是聪明的懒人。
/**
* Register the core class aliases in the container.
*
* @return void
*/
public function registerCoreContainerAliases()
{
$aliases = [
'app' => [IlluminateFoundationApplication::class, IlluminateContractsContainerContainer::class, IlluminateContractsFoundationApplication::class],
'auth' => [IlluminateAuthAuthManager::class, IlluminateContractsAuthFactory::class],
'auth.driver' => [IlluminateContractsAuthGuard::class],
'blade.compiler' => [IlluminateViewCompilersBladeCompiler::class],
'cache' => [IlluminateCacheCacheManager::class, IlluminateContractsCacheFactory::class],
'cache.store' => [IlluminateCacheRepository::class, IlluminateContractsCacheRepository::class],
'config' => [IlluminateConfigRepository::class, IlluminateContractsConfigRepository::class],
'cookie' => [IlluminateCookieCookieJar::class, IlluminateContractsCookieFactory::class, IlluminateContractsCookieQueueingFactory::class],
'encrypter' => [IlluminateEncryptionEncrypter::class, IlluminateContractsEncryptionEncrypter::class],
'db' => [IlluminateDatabaseDatabaseManager::class],
'db.connection' => [IlluminateDatabaseConnection::class, IlluminateDatabaseConnectionInterface::class],
'events' => [IlluminateEventsDispatcher::class, IlluminateContractsEventsDispatcher::class],
'files' => [IlluminateFilesystemFilesystem::class],
'filesystem' => [IlluminateFilesystemFilesystemManager::class, IlluminateContractsFilesystemFactory::class],
'filesystem.disk' => [IlluminateContractsFilesystemFilesystem::class],
'filesystem.cloud' => [IlluminateContractsFilesystemCloud::class],
'hash' => [IlluminateContractsHashingHasher::class],
'translator' => [IlluminateTranslationTranslator::class, IlluminateContractsTranslationTranslator::class],
'log' => [IlluminateLogWriter::class, IlluminateContractsLoggingLog::class, PsrLogLoggerInterface::class],
'mailer' => [IlluminateMailMailer::class, IlluminateContractsMailMailer::class, IlluminateContractsMailMailQueue::class],
'auth.password' => [IlluminateAuthPasswordsPasswordBrokerManager::class, IlluminateContractsAuthPasswordBrokerFactory::class],
'auth.password.broker' => [IlluminateAuthPasswordsPasswordBroker::class, IlluminateContractsAuthPasswordBroker::class],
'queue' => [IlluminateQueueQueueManager::class, IlluminateContractsQueueFactory::class, IlluminateContractsQueueMonitor::class],
'queue.connection' => [IlluminateContractsQueueQueue::class],
'queue.failer' => [IlluminateQueueFailedFailedJobProviderInterface::class],
'redirect' => [IlluminateRoutingRedirector::class],
'redis' => [IlluminateRedisRedisManager::class, IlluminateContractsRedisFactory::class],
'request' => [IlluminateHttpRequest::class, SymfonyComponentHttpFoundationRequest::class],
'router' => [IlluminateRoutingRouter::class, IlluminateContractsRoutingRegistrar::class, IlluminateContractsRoutingBindingRegistrar::class],
'session' => [IlluminateSessionSessionManager::class],
'session.store' => [IlluminateSessionStore::class, IlluminateContractsSessionSession::class],
'url' => [IlluminateRoutingUrlGenerator::class, IlluminateContractsRoutingUrlGenerator::class],
'validator' => [IlluminateValidationFactory::class, IlluminateContractsValidationFactory::class],
'view' => [IlluminateViewFactory::class, IlluminateContractsViewFactory::class],
];
foreach ($aliases as $key => $aliases) {
foreach ($aliases as $alias) {
$this->alias($key, $alias);
}
}
}
这里出现了一个instance函数，其实这并不是Application类的函数，而是Application类的父类Container类的函数
/**
* Register an existing instance as shared in the container.
*
* @param string $abstract
* @param mixed $instance
* @return void
*/
public function instance($abstract, $instance)
{
$this->removeAbstractAlias($abstract);
unset($this->aliases[$abstract]);
// We'll check to determine if this type has been bound before, and if it has
// we will fire the rebound callbacks registered with the container and it
// can be updated with consuming classes that have gotten resolved here.
$this->instances[$abstract] = $instance;
if ($this->bound($abstract)) {
$this->rebound($abstract);
}
}
Application是Container的子类，所以$app不仅是Application类的对象，还是Container的对象，所以，新出现的singleton函数我们就可以到Container类的源代码文件里查。bind函数和singleton的区别见这篇博文。
singleton这个函数，前一个参数是实际类名，后一个参数是类的“别名”。
$app对象声明了3个单例模型对象，分别是HttpKernel，ConsoleKernel，ExceptionHandler。请注意，这里并没有创建对象，只是声明，也只是起了一个“别名”。
大家有没有发现，index.php中也有一个$kernel变量，但是只保存了make出来的HttpKernel变量，因此本文不再讨论，ConsoleKernel，ExceptionHandler。。。
继续在文件夹下找到AppHttpKernel.php，既然我们把实际的HttpKernel做的事情都写在这个php文件里，就从这份代码里看看究竟做了哪些事？
<?php
namespace AppHttp;
use IlluminateFoundationHttpKernel as HttpKernel;
class Kernel extends HttpKernel
{
/**
* The application's global HTTP middleware stack.
*
* These middleware are run during every request to your application.
*
* @var array
*/
protected $middleware = [
IlluminateFoundationHttpMiddlewareCheckForMaintenanceMode::class,
//AppHttpMiddlewareMyMiddleware::class,
];
/**
* The application's route middleware groups.
*
* @var array
*/
protected $middlewareGroups = [
'web' => [
AppHttpMiddlewareEncryptCookies::class,
IlluminateCookieMiddlewareAddQueuedCookiesToResponse::class,
IlluminateSessionMiddlewareStartSession::class,
IlluminateViewMiddlewareShareErrorsFromSession::class,
AppHttpMiddlewareVerifyCsrfToken::class,
],
'api' => [
'throttle:60,1',
],
];
/**
* The application's route middleware.
*
* These middleware may be assigned to groups or used individually.
*
* @var array
*/
protected $routeMiddleware = [
'auth' => AppHttpMiddlewareAuthenticate::class,
'auth.basic' => IlluminateAuthMiddlewareAuthenticateWithBasicAuth::class,
'guest' => AppHttpMiddlewareRedirectIfAuthenticated::class,
'throttle' => IlluminateRoutingMiddlewareThrottleRequests::class,
'mymiddleware'=>AppHttpMiddlewareMyMiddleware::class,
];
}
一目了然，HttpKernel里定义了中间件数组。
该做的做完了，就开始了请求到响应的过程，见index.php
$response = $kernel->handle(
$request = IlluminateHttpRequest::capture()
);
$response->send();
最后在中止，释放所有资源。
/**
* Call the terminate method on any terminable middleware.
*
* @param IlluminateHttpRequest $request
* @param IlluminateHttpResponse $response
* @return void
*/
public function terminate($request, $response)
{
$this->terminateMiddleware($request, $response);
$this->app->terminate();
}
总结一下，简单归纳整个过程就是：
1.index.php加载ootstrapapp.php，在Application类的构造函数中创建Container，注册了ServiceProvider，定义了别名数组，然后用app变量保存构造函数构造出来的对象。
2.使用app这个对象，创建1个单例模式的对象HttpKernel，在创建HttpKernel时调用了构造函数，完成了中间件的声明。
3.以上这些工作都是在请求来访之前完成的，接下来开始等待请求，然后就是：接受到请求-->处理请求-->发送响应-->中止app变量