Asp.net MVC-3-执行过程

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