Asp.net MVC-3-执行过程

来源:转载

本篇主要讲述MVC处理请求时创建Controller和执行Action的完整过程。

创建Controller

先查看MvcHandler中处理请求的方法BeginProcessRequest:

protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state){IController controller;IControllerFactory factory;ProcessRequestInit(httpContext, out controller, out factory);IAsyncController asyncController = controller as IAsyncController;if (asyncController != null){ ……}else{ ……} }

再查看其中创建Controller的方法ProcessRequestInit

private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory){HttpContext currentContext = HttpContext.Current;……AddVersionHeader(httpContext);RemoveOptionalRoutingParameters();string controllerName = RequestContext.RouteData.GetRequiredString("controller");factory = ControllerBuilder.GetControllerFactory();controller = factory.CreateController(RequestContext, controllerName);……}

Controller通过ControllerBuilder属性的方法GetControllerFactory获取到ControllerFactory对象然后由ControllerFactory创建,ControllerBuilder属性定义如下。

internal ControllerBuilder ControllerBuilder{get{ if (_controllerBuilder == null) {_controllerBuilder = ControllerBuilder.Current; } return _controllerBuilder;}set { _controllerBuilder = value; }}

可知ControllerBuilder默认使用ControllerBuilder.Current,查看ControllerBuilder类的代码:

public IControllerFactory GetControllerFactory(){return _serviceResolver.Current;}internal ControllerBuilder(IResolver<IControllerFactory> serviceResolver){_serviceResolver = serviceResolver ?? new SingleServiceResolver<IControllerFactory>( () => _factoryThunk(),new DefaultControllerFactory { ControllerBuilder = this },"ControllerBuilder.GetControllerFactory");}

可知默认返回的ControllerFactory为DefaultControllerFactory(当然我们也可以注册默认的自定义的ControllerFactory),这里我们可继续查看DefaultControllerFactory

internal DefaultControllerFactory(……){…… _activatorResolver = activatorResolver ?? new SingleServiceResolver<IControllerActivator>( () => null, new DefaultControllerActivator(dependencyResolver), "DefaultControllerFactory constructor");}}private IControllerActivator ControllerActivator{get{ if (_controllerActivator != null) {return _controllerActivator; } _controllerActivator = _activatorResolver.Current; return _controllerActivator;}}public virtual IController CreateController(RequestContext requestContext, string controllerName){……Type controllerType = GetControllerType(requestContext, controllerName);IController controller = GetControllerInstance(requestContext, controllerType);return controller;}protected internal virtual IController GetControllerInstance(RequestContext requestContext, Type controllerType){……return ControllerActivator.Create(requestContext, controllerType);}

可以看到最终Controller由DefaultControllerActivator来创建

public DefaultControllerActivator(IDependencyResolver resolver){ if (resolver == null) {_resolverThunk = () => DependencyResolver.Current; } else {_resolverThunk = () => resolver; }} public IController Create(RequestContext requestContext, Type controllerType){ try {return (IController)(_resolverThunk().GetService(controllerType) ?? Activator.CreateInstance(controllerType)); } catch (Exception ex) {throw new InvalidOperationException(String.Format( CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ErrorCreatingController, controllerType),ex); }}

到此为止Controller就被创建出来了,这里我们看到了DependencyResolver.Current,这是MVC的默认注入容器,如果设置了容器,Controller的创建就可以通过容器(GetService)来完成了,如果未实现DependencyResolver或DependencyResolver未注册该Controller则通过反射来创建(使用Activator.CreateInstance,必须存在无参构造函数)。

Controller注入

下面来看对框架的第一个扩展也是最基本的扩展:为框架提供Ioc容器并注册Controller。对于Ioc容器的起源和作用这里就不多讲了。目前Ioc的思想已经普遍地应用于各种开发实践当中了,特别是企业应用开发中,Spring已经是Java开发事实上的基础框架。Asp.net Mvc也深受影响,虽然框架本身没有提供Ioc容器的实现,但是提供了很方便的扩展方式,通过扩展我们不仅可以使用容器管理自定义的对象,甚至可以将对象注入到Mvc框架当中(简单的比如对Controller的注入)。因为Mvc框架默认首先通过容器来获取对象,然后才是框架提供的方式(一般是一种默认实现),在以后的分析中可以看到许多的源码都可以证实这一点。

下面我们通过添加Autofac来实现依赖注入。

首先通过nuget添加Autofac和Autofac.Mvc5的引用。

在App_Start目录下添加Autofac的初始化类如下:

public class AutofacConfig{public static IDependencyResolver GeResolver(){var builder = new ContainerBuilder();Registers(builder);builder.RegisterControllers(Assembly.GetExecutingAssembly());return new AutofacDependencyResolver(builder.Build());} private static void Registers(ContainerBuilder builder){ }}

然后在Global.asax的Application_Start方法中添加代码如下:

DependencyResolver.SetResolver(AutofacConfig.GeResolver());

这样我们就完成了依赖注入(目前只是Controller的注入,当然以后可以AutofacConfig 的Registers方法中把我们需要注入的对象注入到Autofac容器中)。关于依赖注入需要注意的主要有两点:一个是ContainerBuilder的扩展方法RegisterControllers,其参数类型为params Assembly[]可以传入一个或多个Assembly然后注册这些Assembly里的Controller,这样我们就可以将Controller放到不同的工程里;另一个是DependencyResolver.SetResolver,这样会替换掉默认的DependencyResolver实现,我们正是通过这样把Autofac容器作为了Mvc的容器从而完成依赖注入。

下面通过一个简单的例子说明Ioc容器的应用。首先创建一个简单的接口及其实现的类

public interface IIocTest {string Say(); } public class IocTest: IIocTest {public string Say(){return "IocTest";}}

然后再HomeController中添加一个该接口的字段,并创建一个构造函数用于注入(AutoFac默认只支持构造函数注入,但也可以开启属性注入)。    

 private IIocTest iocTestInsatnce; public HomeController(IIocTest iocTest) {iocTestInsatnce = iocTest; }

然后再一个Action中调用接口方法,然后通过ViewBag(或其它方法)将其传到页面并显示,页面显示有多种方法,这里直接加到标题中:

 public ActionResult Index() {ViewBag.iocSays = iocTestInsatnce.Say();return View(); }
@{ViewBag.Title = "Home Page"+ ViewBag.iocSays;}

然后运行程序,查看相应页面的标题,验证注入是否成功。

执行Action

创建好Controller之后我们再来看Controller是如何执行请求的。

首先看ControllerBase,这是所有Controller的基类,查看它的处理方法BeginExecuteCore。

protected virtual IAsyncResult BeginExecuteCore(AsyncCallback callback, object state){……try{ string actionName = GetActionName(RouteData); IActionInvoker invoker = ActionInvoker; IAsyncActionInvoker asyncInvoker = invoker as IAsyncActionInvoker; if (asyncInvoker != null) {BeginInvokeDelegate<ExecuteCoreState> beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState, ExecuteCoreState innerState){return innerState.AsyncInvoker.BeginInvokeAction(innerState.Controller.ControllerContext, innerState.ActionName, asyncCallback, asyncState);};EndInvokeVoidDelegate<ExecuteCoreState> endDelegate = delegate(IAsyncResult asyncResult, ExecuteCoreState innerState){if (!innerState.AsyncInvoker.EndInvokeAction(asyncResult)){ innerState.Controller.HandleUnknownAction(innerState.ActionName);}};ExecuteCoreState executeState = new ExecuteCoreState() { Controller = this, AsyncInvoker = asyncInvoker, ActionName = actionName };return AsyncResultWrapper.Begin(callback, state, beginDelegate, endDelegate, executeState, _executeCoreTag); } else { …… }}……}

可以看到Action的执行通过ActionInvoker. BeginInvokeAction实现,ActionInvoker的获取方式如下:

protected virtual IActionInvoker CreateActionInvoker(){return Resolver.GetService<IAsyncActionInvoker>() ?? Resolver.GetService<IActionInvoker>() ?? new AsyncControllerActionInvoker();}

这里也看到了Resolver即可以通过Ioc容器来提供IAsyncActionInvoker或IActionInvoker,如果未提供则使用默认的AsyncControllerActionInvoker,再查看默认的实现AsyncControllerActionInvoker的处理方法BeginInvokeAction。

public virtual IAsyncResult BeginInvokeAction(ControllerContext controllerContext, string actionName, AsyncCallback callback, object state){if (controllerContext == null){ throw new ArgumentNullException("controllerContext");}Contract.Assert(controllerContext.RouteData != null);if (String.IsNullOrEmpty(actionName) && !controllerContext.RouteData.HasDirectRouteMatch()){ throw Error.ParameterCannotBeNullOrEmpty("actionName");}ControllerDescriptor controllerDescriptor = GetControllerDescriptor(controllerContext);ActionDescriptor actionDescriptor = FindAction(controllerContext, controllerDescriptor, actionName);if (actionDescriptor != null){ FilterInfo filterInfo = GetFilters(controllerContext, actionDescriptor); Action continuation = null; BeginInvokeDelegate beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState) {try{AuthenticationContext authenticationContext = InvokeAuthenticationFilters(controllerContext, filterInfo.AuthenticationFilters, actionDescriptor);if (authenticationContext.Result != null){ AuthenticationChallengeContext challengeContext =InvokeAuthenticationFiltersChallenge(controllerContext,filterInfo.AuthenticationFilters, actionDescriptor, authenticationContext.Result); continuation = () => InvokeActionResult(controllerContext,challengeContext.Result ?? authenticationContext.Result);}else{ AuthorizationContext authorizationContext = InvokeAuthorizationFilters(controllerContext, filterInfo.AuthorizationFilters, actionDescriptor); if (authorizationContext.Result != null) {AuthenticationChallengeContext challengeContext =InvokeAuthenticationFiltersChallenge(controllerContext,filterInfo.AuthenticationFilters, actionDescriptor, authorizationContext.Result);continuation = () => InvokeActionResult(controllerContext,challengeContext.Result ?? authorizationContext.Result); } else {if (controllerContext.Controller.ValidateRequest){ValidateRequest(controllerContext);}IDictionary<string, object> parameters = GetParameterValues(controllerContext, actionDescriptor);IAsyncResult asyncResult = BeginInvokeActionMethodWithFilters(controllerContext, filterInfo.ActionFilters, actionDescriptor, parameters, asyncCallback, asyncState);continuation = () =>{ActionExecutedContext postActionContext = EndInvokeActionMethodWithFilters(asyncResult);AuthenticationChallengeContext challengeContext = InvokeAuthenticationFiltersChallenge(controllerContext, filterInfo.AuthenticationFilters, actionDescriptor, postActionContext.Result);InvokeActionResultWithFilters(controllerContext, filterInfo.ResultFilters, challengeContext.Result ?? postActionContext.Result);};return asyncResult; }}}catch (ThreadAbortException){throw;}catch (Exception ex){ExceptionContext exceptionContext = InvokeExceptionFilters(controllerContext, filterInfo.ExceptionFilters, ex);if (!exceptionContext.ExceptionHandled){ throw;}continuation = () => InvokeActionResult(controllerContext, exceptionContext.Result);}return BeginInvokeAction_MakeSynchronousAsyncResult(asyncCallback, asyncState); }; EndInvokeDelegate<bool> endDelegate = delegate(IAsyncResult asyncResult) {try{continuation();}catch (ThreadAbortException){throw;}catch (Exception ex){ExceptionContext exceptionContext = InvokeExceptionFilters(controllerContext, filterInfo.ExceptionFilters, ex);if (!exceptionContext.ExceptionHandled){ throw;}InvokeActionResult(controllerContext, exceptionContext.Result);}return true; }; return AsyncResultWrapper.Begin(callback, state, beginDelegate, endDelegate, _invokeActionTag);}else{ return BeginInvokeAction_ActionNotFound(callback, state);}}

这是一个非常重要的方法,也是我们后续分析的基础,它描述了我们主要的处理流程。此方法中关联了相当多的类,但是其主要处理流程是容易清晰明白的。大致是先获取ControllerDescriptor和ActionDescriptor,然后依次执行Action中的过滤器AuthenticationFilters、AuthorizationFilters来进行验证和授权检查,然后是页面安全检查、获取参数,然后执行ActionFilter和Action,整个过程中如果设置了Result会直接执行AuthenticationFilters的AuthenticationFiltersChallenge,然后执行ResultFilters对结果进行过滤,当然如果处理过程中抛出异常会调用ExceptionFilter进行处理。如果要理解处理的细节需要查看大量的源码,这里提供一点小小的参考ReflectedActionDescriptor、ReflectedControllerDescriptor为ActionDescriptor和ControllerDescriptor的默认实现,Action、过滤器等的查找实际都是通过反射类获取的。

下面为BeginInvokeAction的处理过程图

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