MVC源码分析

上一篇, 出现了一个至关重要的类:MvcHandler, 接下来就来看一下MvcHandler吧. 先不看具体方法, 先看一下类里面的情况.

//这里实现了两个重要的接口, 异步处理和同步处理的接口
public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState
{
    // Fields
    private ControllerBuilder _controllerBuilder;
    private static readonly object _processRequestTag;
    internal static readonly string MvcVersion;
    public static readonly string MvcVersionHeaderName;

    // Methods
    static MvcHandler();
    public MvcHandler(RequestContext requestContext);
    protected internal virtual void AddVersionHeader(HttpContextBase httpContext);
    protected virtual IAsyncResult BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, object state);
    protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state);
    protected internal virtual void EndProcessRequest(IAsyncResult asyncResult);
    private static string GetMvcVersionString();
    protected virtual void ProcessRequest(HttpContext httpContext);
    protected internal virtual void ProcessRequest(HttpContextBase httpContext);
    private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory);
    private void RemoveOptionalRoutingParameters();
    IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData);
    void IHttpAsyncHandler.EndProcessRequest(IAsyncResult result);
    void IHttpHandler.ProcessRequest(HttpContext httpContext);

    // Properties
    internal ControllerBuilder ControllerBuilder { get; set; }
    public static bool DisableMvcResponseHeader { get; set; }
    protected virtual bool IsReusable { get; }
    public RequestContext RequestContext { get; private set; }
    bool IHttpHandler.IsReusable { get; }
}

从上面看, 有两种执行方式, 一种是同步的, 一种是异步的. 那默认情况下, 其实会走异步的方式. 但是这里呢, 我想用同步的方式去分析, 其实过程原理都是一样的, 只是方式不同.

一、解析

注意到这个类, 实现了三个接口, 那第三个接口是干啥的呢? 先看一下这个接口的内容.

public interface IRequiresSessionState
{
}

点进去, 发现这个接口没有任何方法, 那么他是干什么的呢? 

其实他是一种标志, 或者叫标记, 表示这个类有对Session的访问权限, 包括读写. 如果你想自定义Http处理程序, 又想操作Session的话, 记得实现这个接口.

接下来, 回归正题了.  来看一下这里的 PR 方法.

protected virtual void ProcessRequest(HttpContext httpContext)
{
    HttpContextBase base2 = new HttpContextWrapper(httpContext);
    this.ProcessRequest(base2);
}

protected internal virtual void ProcessRequest(HttpContextBase httpContext)
{
    IController controller;
    IControllerFactory factory;
    this.ProcessRequestInit(httpContext, out controller, out factory);
    try
    {
        controller.Execute(this.RequestContext);
    }
    finally
    {
        factory.ReleaseController(controller);
    }
}

这里也就只有三个方法了, 我们一个一个分析.

1. ProcessRequestInit()

//MvcHandler
private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory)
{
    HttpContext current = HttpContext.Current;
    if ((current != null) && (ValidationUtility.IsValidationEnabled(current) == true))
    {
        ValidationUtility.EnableDynamicValidation(current);
    }
　　 //添加 Http Header : HTTP/1.1 200 OK ......
    this.AddVersionHeader(httpContext);
    this.RemoveOptionalRoutingParameters();
　　 //从路由中获取控制器的名称
    string requiredString = this.RequestContext.RouteData.GetRequiredString("controller");
　　 //获取控制器工厂
    factory = this.ControllerBuilder.GetControllerFactory();
　　 //利用控制器工厂创建控制器类
    controller = factory.CreateController(this.RequestContext, requiredString);
    if (controller == null)
    {
        throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture, 
　　　　　　MvcResources.ControllerBuilder_FactoryReturnedNull, new object[] { factory.GetType(), requiredString }));
    }
}

1.1 从路由中获取控制器名称 - GetRequiredString

public string GetRequiredString(string valueName)
{
    object obj2;
    if (this.Values.TryGetValue(valueName, out obj2))
    {
        string str = obj2 as string;
        if (!string.IsNullOrEmpty(str))
        {
            return str;
        }
    }
    throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, 
　　　　SR.GetString("RouteData_RequiredValue"), new object[] { valueName }));
}

1.2 获取创建工厂 - GetControllerFactory

public IControllerFactory GetControllerFactory()
{
    return this._serviceResolver.Current;
}

1.3 创建控制器类 - CreateController

//DefaultControllerFactory类
public virtual IController CreateController(RequestContext requestContext, string controllerName)
{
    if (requestContext == null)
    {
        throw new ArgumentNullException("requestContext");
    }
    if (string.IsNullOrEmpty(controllerName))
    {
        throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
    }
    Type controllerType = this.GetControllerType(requestContext, controllerName);
    return this.GetControllerInstance(requestContext, controllerType);
}

1.3.1 GetControllerType()

protected internal virtual Type GetControllerType(RequestContext requestContext, string controllerName)
{
    object obj2;
    Type type;
    if (string.IsNullOrEmpty(controllerName))
    {
        throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
    }
    if ((requestContext != null) && requestContext.RouteData.DataTokens.TryGetValue("Namespaces", out obj2))
    {
        IEnumerable<string> source = obj2 as IEnumerable<string>;
        if ((source != null) && source.Any<string>())
        {
            HashSet<string> namespaces = new HashSet<string>(source, StringComparer.OrdinalIgnoreCase);
            type = this.GetControllerTypeWithinNamespaces(requestContext.RouteData.Route, controllerName, namespaces);
            if (type == null)
            {
                bool flag = false;
                if (!flag.Equals(requestContext.RouteData.DataTokens["UseNamespaceFallback"]))
                {
                    goto Label_0092;
                }
            }
            return type;
        }
    }
Label_0092:
    if (this.ControllerBuilder.DefaultNamespaces.Count > 0)
    {
        HashSet<string> set2 = new HashSet<string>(this.ControllerBuilder.DefaultNamespaces, 
　　　　　　StringComparer.OrdinalIgnoreCase);
        type = this.GetControllerTypeWithinNamespaces(requestContext.RouteData.Route, controllerName, set2);
        if (type != null)
        {
            return type;
        }
    }
    return this.GetControllerTypeWithinNamespaces(requestContext.RouteData.Route, controllerName, null);
}

这里会从路由中, 获取控制器所在的命名空间, 有一点需要注意, 尽量不要在不同的namespace里面命名相同的控制器,不管有这个限制还是没有这个限制, 都是能正常创建控制器的(不重名的情况下). 先看这里.

private Type GetControllerTypeWithinNamespaces(RouteBase route, string controllerName, HashSet<string> namespaces)
{
　　 //MVC-ControllerTypeCache.xml文件中获取Controller的缓存
    this.ControllerTypeCache.EnsureInitialized(this.BuildManager);
　　 //从之前获取的缓存中, 来获取控制器的类型
    ICollection<Type> controllerTypes = this.ControllerTypeCache.GetControllerTypes(controllerName, namespaces);
    switch (controllerTypes.Count)
    {
        case 0:
            return null;

        case 1:
            return controllerTypes.First<Type>();
    }
    throw CreateAmbiguousControllerException(route, controllerName, controllerTypes);
}

 1.3.2 GetControllerInstance()

protected internal virtual IController GetControllerInstance(RequestContext requestContext, Type controllerType)
{
    if (controllerType == null)
    {
        throw new HttpException(0x194, 
　　　　　　string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_NoControllerFound, 　　
　　　　　　new object[] { requestContext.HttpContext.Request.Path }));
    }
    if (!typeof(IController).IsAssignableFrom(controllerType))
    {
        throw new ArgumentException(　　
　　　　　　string.Format(CultureInfo.CurrentCulture, 
　　　　　　MvcResources.DefaultControllerFactory_TypeDoesNotSubclassControllerBase, 
　　　　　　new object[] { controllerType }), "controllerType");
    }
    return this.ControllerActivator.Create(requestContext, controllerType);
}

来看一下这里的Create方法, 看一下具体是怎么创建的.

public IController Create(RequestContext requestContext, Type controllerType)
{
    IController controller;
    try
    {
        controller = (IController) (this._resolverThunk().GetService(controllerType) ?? 
　　　　　　Activator.CreateInstance(controllerType));
    }
    catch (Exception exception)
    {
        throw new InvalidOperationException(
　　　　　　string.Format(CultureInfo.CurrentCulture, MvcResources.DefaultControllerFactory_ErrorCreatingController, 
　　　　　　new object[] { controllerType }), exception);
    }
    return controller;
}

这里有一个扩展点, 像之前篇幅提到的Autofac Mvc部分, 在这里, 反馈的GetService(controllerType)就不是一个空值了.

如果没有搜索到这些扩展, 就会默认反射的方式来创建控制器.

Demo: 值的注意的是, 这些扩展都是要实现 IDependencyResolve 接口的, 此例子是从Autofac.Integration.Mvc.dll中来的

public class AutofacDependencyResolver : IDependencyResolver
{
    // Fields
    private readonly Action<ContainerBuilder> _configurationAction;
    private readonly ILifetimeScope _container;
    private ILifetimeScopeProvider _lifetimeScopeProvider;

    // Methods
    public AutofacDependencyResolver(ILifetimeScope container);
    public AutofacDependencyResolver(ILifetimeScope container, ILifetimeScopeProvider lifetimeScopeProvider);
    public AutofacDependencyResolver(ILifetimeScope container, Action<ContainerBuilder> configurationAction);
    public AutofacDependencyResolver(ILifetimeScope container, 
　　　　ILifetimeScopeProvider lifetimeScopeProvider, 
　　　　Action<ContainerBuilder> configurationAction);
    public object GetService(Type serviceType);
    public IEnumerable<object> GetServices(Type serviceType);

    // Properties
    public ILifetimeScope ApplicationContainer { get; }
    public static AutofacDependencyResolver Current { get; }
    public ILifetimeScope RequestLifetimeScope { get; }
}

2. Execute()

这里执行的是ControllerBase的Execute方法. 是一个虚方法. 这里的方法, 留到下一篇分析了.

protected virtual void Execute(RequestContext requestContext)
{
    if (requestContext == null)
    {
        throw new ArgumentNullException("requestContext");
    }
    if (requestContext.HttpContext == null)
    {
        throw new ArgumentException(MvcResources.ControllerBase_CannotExecuteWithNullHttpContext, "requestContext");
    }
    this.VerifyExecuteCalledOnce();
　　 //在这里创建了控制器上下文, ControllerContext
    this.Initialize(requestContext);
    using (ScopeStorage.CreateTransientScope())
    {
　　　　  //加载 TempData, 创建及执行 Action, 处理 Action 返回的 ActionResult, 保存TempData数据
        this.ExecuteCore();
    }
}

3. ReleaseController()

这个方法, 顾名思义, 是释放资源的. 来看一下, DefaultControllerFactory 类中的此方法

public virtual void ReleaseController(IController controller)
{
    IDisposable disposable = controller as IDisposable;
    if (disposable != null)
    {
        disposable.Dispose();
    }
}

 从上面的分析, 基本可以看到控制器的创建过程, 至于他的执行过程, 就放到下一篇去了, 内容还是很多的.

二、扩展

从上面的分析能看到这里有一个依赖注入扩展, 那么下面, 就这个依赖注入扩展, 来举一个小例子.(残破的例子, 别介意, 能演示功能的)

用的Autofac, 不过与上面不同, 并没有引用上面的程序集, 只引用Autofac.dll一个程序集就可以了.

我先从之前Autofac篇章, 弄了一个Helper类过来, 精简一下.

public class IocContainer
{
    private static ContainerBuilder builder;

    private static IContainer container;

    static IocContainer()
    {
        builder = new ContainerBuilder();
    }

    public static void RegisterTypes(params Type[] types)
    {
        builder.RegisterTypes(types);
    }

    public static void Build()
    {
        container = builder.Build();
    }

    public static object Create(Type t)
    {
        return container.Resolve(t);
    }
}

然后, 我建了一个Resolver.

public class MyDependencyResolver : IDependencyResolver
{
    public object GetService(Type serviceType)
    {
        bool flag = true;
        string path = @"F:MVC解析MyControllerFac1.txt";
        if (!File.Exists(path))
        {
            File.Create(path).Close();
        }

        try
        {
            return IocContainer.Create(serviceType);
        }
        catch (Exception)
        {
            flag = false;
            //这里需要注意, 需要返回一个null值, 否则会报错
            return null;
        }
        finally
        {
            using (FileStream fs = new FileStream(path, FileMode.Append))
            {
                var msg = flag ? "命中" : "飘过";
                byte[] bt = System.Text.Encoding.UTF8.GetBytes(serviceType.ToString() + " : " + msg + "
");
                fs.Write(bt, 0, bt.Length);
　　　　　　　 　　 fs.Close();
            }
        }
    }

    public IEnumerable<object> GetServices(Type serviceType)
    {
        var res = new List<object>();
        try
        {
            var obj = IocContainer.Create(serviceType);
            res.Add(obj);
        }
        catch (Exception)
        {

        }
        return res;
    }
}

现在前置工作做好了, 可以去MVC中, 注册我自己的方法了.

protected void Application_Start()
{
    AreaRegistration.RegisterAllAreas();

    WebApiConfig.Register(GlobalConfiguration.Configuration);
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
    RouteConfig.RegisterRoutes(RouteTable.Routes);
    BundleConfig.RegisterBundles(BundleTable.Bundles);
　　 
　　 //这里我就省懒了, 并没有写到单独的方法中取
    IocContainer.RegisterTypes(System.Reflection.Assembly.Load("MyMvc").GetTypes());

    IocContainer.Build();

    DependencyResolver.SetResolver(new MyDependencyResolver());
}

OK, 万事俱备, 只差测试. 跑起来吧

页面能正常访问, 那么是不是走的我哪里呢? 从页面上肯定看不出来, 所以我加了点东西, 看一下1.txt

 从这里来看, 并不是只有 HomeController 走了我自定义的那个方式, 这也是为什么一定要返回一个null了. 对于这些飘过的, 就只能使用MVC默认的方式了. 还是很神奇的.

目录已同步