本文实例讲述了Laravel框架生命周期与原理。分享给大家供大家参考，具体如下：
引言：
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！
正文：
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。
<?phprequire __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, $response);
作者在注释里谈了kernel的作用，kernel的作用，kernel处理来访的请求，并且发送相应返回给用户浏览器。
这里又涉及到了一个app对象，所以附上app对象，所以附上app对象的源码，这份源码是ootstrapapp.php
<?php/*|--------------------------------------------------------------------------| Create The Application|--------------------------------------------------------------------------|| The first thing we will do is create a new Laravel application instance| which serves as the "glue" for all the components of Laravel, and is| the IoC container for the system binding all of the various parts.|*/$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？
<?phpnamespace 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
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希望本文所述对大家基于Laravel框架的PHP程序设计有所帮助。
