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Symfoy2源码分析——启动过程2
上一篇分析Symfony2框架源码，探究Symfony2如何完成一个请求的前半部分，前半部分可以理解为Symfony2框架为处理请求做准备工作，包括container生成、缓存、bundls初始化等一些列准备工作（Symfoy2源码分析——启动过程1）。而这一篇讲的是Symfony2如何根据请求的数据生成Response对象，向客户端返回响应数据。
在分析前需要了解Symfony2的事件驱动机制：Symfony2事件驱动。
言归正传，Symfony2请求的工作流程其实是Symfony2内核的事件驱动完成的，下面是Symfony2框架定义好的内核事件：
final class KernelEvents{ /** * The REQUEST event occurs at the very beginning of request * dispatching * * This event allows you to create a response for a request before any * other code in the framework is executed. The event listener method * receives a Symfony\Component\HttpKernel\Event\GetResponseEvent * instance. * * @var string * * @api */ const REQUEST = ‘kernel.request‘; /** * The EXCEPTION event occurs when an uncaught exception appears * * This event allows you to create a response for a thrown exception or * to modify the thrown exception. The event listener method receives * a Symfony\Component\HttpKernel\Event\GetResponseForExceptionEvent * instance. * * @var string * * @api */ const EXCEPTION = ‘kernel.exception‘; /** * The VIEW event occurs when the return value of a controller * is not a Response instance * * This event allows you to create a response for the return value of the * controller. The event listener method receives a * Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent * instance. * * @var string * * @api */ const VIEW = ‘kernel.view‘; /** * The CONTROLLER event occurs once a controller was found for * handling a request * * This event allows you to change the controller that will handle the * request. The event listener method receives a * Symfony\Component\HttpKernel\Event\FilterControllerEvent instance. * * @var string * * @api */ const CONTROLLER = ‘kernel.controller‘; /** * The RESPONSE event occurs once a response was created for * replying to a request * * This event allows you to modify or replace the response that will be * replied. The event listener method receives a * Symfony\Component\HttpKernel\Event\FilterResponseEvent instance. * * @var string * * @api */ const RESPONSE = ‘kernel.response‘; /** * The TERMINATE event occurs once a response was sent * * This event allows you to run expensive post-response jobs. * The event listener method receives a * Symfony\Component\HttpKernel\Event\PostResponseEvent instance. * * @var string */ const TERMINATE = ‘kernel.terminate‘; /** * The FINISH_REQUEST event occurs when a response was generated for a request. * * This event allows you to reset the global and environmental state of * the application, when it was changed during the request. * * @var string */ const FINISH_REQUEST = ‘kernel.finish_request‘;}
我们可以编写事件监听器，监听相应的内核事件，在Symfony2触发该事件的时候，相应的事件监听器就会执行。监听和唤醒形象的描述，就像，你（事件监听器）参加校运会，去大会（Symfony2）登记（监听）参加50米短跑（事件），当50米短跑比赛开始了（事件被触发），那你就奔跑吧（监听器执行，其实就是一个执行函数，函数完成什么工作就取决于你的需求了），少年。
Symfony2的内核事件处理流程大部分工作都在HttpKernel::handleRaw方法中：
1 private function handleRaw(Request $request, $type = self::MASTER_REQUEST) 2 { 3 $this->requestStack->push($request); 4 5 // request 6 // 初始化事件，事件对象会被传递给监听器，所以事件可以说是一个信息的载体，事件内存放着监听器感兴趣的数据。 7 $event = new GetResponseEvent($this, $request, $type); 8 // 触发kernel.request事件，后续详细讲解EventDispatcher::dispatch方法的实现， 9 // 这里我们需要知道的是，dispatcher把$event传递给所有监听了kernel.request事件的监听器，监听器将会执行。10 // kernel.request事件发生在controller执行之前，我们可以在这一步奏完成路由解析等为controller执行提供准备数据，11 // 在这个过程允许我们直接生成Response对象，向客户端输出数据，那么controller就不会被执行了。12 $this->dispatcher->dispatch(KernelEvents::REQUEST, $event);13 14 // 如果我们在kernel.request事件生成了Response对象（响应数据），那么就跳过kernel.controller、kernel.view事件、15 // controller也会被跳过，直接执行kernel.response事件。16 if ($event->hasResponse()) {17 return $this->filterResponse($event->getResponse(), $request, $type);18 }19 20 // load controller21 // 根据路由规则返回 一个对象或者数组或者字符串 ，如果$controller是一个数组，$controller[0]是存放的是要执行的controller对象，22 // $controller[0]存放的是controller对象执行的方法，即action，方法的参数没有保存在$controller数组中；23 // 如果$controller是对象，那么该对象就实现了__invoke 方法；24 // 如果$controller是字符串，那么$controller就是要运行的函数的函数名。25 // 图2是$controller的一个var_dump例子26 if (false === $controller = $this->resolver->getController($request)) {27 throw new NotFoundHttpException(sprintf(‘Unable to find the controller for path "%s". Maybe you forgot to add the matching route in your routing configuration?‘, $request->getPathInfo()));28 }29 30 $event = new FilterControllerEvent($this, $controller, $request, $type);31 // 触发kernel.controller事件，这个事件发生在controller执行前。我们可以通过监听这个事件在controller执行前修改controller，32 // 或者完成一些动作。33 $this->dispatcher->dispatch(KernelEvents::CONTROLLER, $event);34 $controller = $event->getController();35 36 // controller arguments37 // 从request对象中获取controller方法的参数38 $arguments = $this->resolver->getArguments($request, $controller);39 40 // call controller41 // 执行controller42 $response = call_user_func_array($controller, $arguments);43 44 // view45 // 如果$response不是Response对象，那么kernel.view事件就会触发，监听kernel.view事件的监听器通过$response值生成Response对象。46 if (!$response instanceof Response) {47 $event = new GetResponseForControllerResultEvent($this, $request, $type, $response);48 $this->dispatcher->dispatch(KernelEvents::VIEW, $event);49 50 if ($event->hasResponse()) {51 $response = $event->getResponse();52 }53 54 if (!$response instanceof Response) {55 $msg = sprintf(‘The controller must return a response (%s given).‘, $this->varToString($response));56 57 // the user may have forgotten to return something58 if (null === $response) {59 $msg .= ‘ Did you forget to add a return statement somewhere in your controller?‘;60 }61 throw new \LogicException($msg);62 }63 }64 65 // 触发kernel.response事件，在向客户端输出Response对象前，我们可以对Response对象进行修改，66 // 例如修改response头部，设置缓存、压缩输出数据等。67 68 // 接着触发kernel.finish_request事件，把当前请求从请求栈中弹出，当前请求就完成。69 return $this->filterResponse($response, $request, $type);70 71 // 千万别忘记了，filterResponse执行完后，Symfony2内核事件处理流程还有最后一步，位于app_dev.php[app.php]最后一行，72 // $kernel->terminate($request, $response);这个方法触发kernel.terminate事件，此时，Symfony2已经响应了客户端的请求，73 // 向客户端输出了Response对象。监听kernel.terminate事件的监听器，主要是为了完成一些耗时的操作，操作的结果不需要返回给74 // 客户端的，例如邮件发送、图片压缩等等。75 // 到这里，Symfony2的整个流程就走完了。76 }
HttpKernel::filterResponse方法和HttpKernel::finishRequest方法:1 private function filterResponse(Response $response, Request $request, $type) 2 { 3 $event = new FilterResponseEvent($this, $request, $type, $response); 4 5 $this->dispatcher->dispatch(KernelEvents::RESPONSE, $event); 6 7 $this->finishRequest($request, $type); 8 9 return $event->getResponse();10 }11 12 /**13 * Publishes the finish request event, then pop the request from the stack.14 *15 * Note that the order of the operations is important here, otherwise16 * operations such as {@link RequestStack::getParentRequest()} can lead to17 * weird results.18 *19 * @param Request $request20 * @param int $type21 */22 private function finishRequest(Request $request, $type)23 {24 $this->dispatcher->dispatch(KernelEvents::FINISH_REQUEST, new FinishRequestEvent($this, $request, $type));25 $this->requestStack->pop();26 }
图2
Symfony2框架的事件分发机制的核心代码：
1 public function dispatch($eventName, Event $event = null) 2 { 3 if (null === $event) { 4 $event = new Event(); 5 } 6 7 $event->setDispatcher($this); 8 $event->setName($eventName); 9 10 if (!isset($this->listeners[$eventName])) {11 return $event;12 }13 14 // $eventName即：KernelEvents::REQUEST、KernelEvents::CONTROLLER、KernelEvents::VIEW、KernelEvents::RESPONSE、KernelEvents::TERMINATE等15 // getListeners返回所有监听$eventName事件的监听器16 $this->doDispatch($this->getListeners($eventName), $eventName, $event);17 18 return $event;19 }20 21 protected function doDispatch($listeners, $eventName, Event $event)22 {23 // 监听器执行24 foreach ($listeners as $listener) {25 call_user_func($listener, $event, $eventName, $this);26 // 如果其中一个监听器把$event的propagationStopped属性设置为true，那么表示$eventName这一事件终止执行，27 // 事件不会往$listeners里尚未执行的监听器传递该事件。28 if ($event->isPropagationStopped()) {29 break;30 }31 }32 }
Symfoy2源码分析——启动过程2
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