ASP.NET Web API 框架研究 Controller创建 HttpController 类型解析 选择 创建

　　上一篇介绍了HttpController的一些细节，接下来说下HttpController 类型解析、选择和创建。生产HttpController实例的生产线如下图：

　　

一、涉及的类及源码分析

　　涉及的类主要在程序集System.Web.Http中的Dispatcher下边，类如下图：

　　

1、IAssembliesResolver DefaultAssembliesResolver

　　AssembliesResolver为HttpController类型的解析提供了可选的程序集，即提供了实现了IHttpController接口的候选HttpController类型的程序集范围；所有AssembliesResolver都实现IAssembliesResolver，接口只有一个方法，如下

  public interface IAssembliesResolver
    {
        //提供解析的程序集范围，返回应用程序可用的程序集列表
        ICollection<Assembly> GetAssemblies();
    }

　　默认实现是DefauItAssembliesResolver，DefauItAssembliesResolver在实现的GetAssembIies方法中直接返回当前应用程序域加载的所有程序集列表，代码如下

  public class DefaultAssembliesResolver : IAssembliesResolver
    {
        public virtual ICollection<Assembly> GetAssemblies()
        {
            return AppDomain.CurrentDomain.GetAssemblies().ToList();
        }
    }

　　而服务接口IAssembliesResolver的服务实例DefauItAssembliesResolver，是在服务容器里注册的

　　获取可以用扩展方法直接获取：

　　

　

 2、IHttpControllerTypeResolver DefaultHttpControllerTypeResolver

　　返回可供选择的HttpControllerType列表。

　　前边的AssembIiesResolver对象为HttpController类型的解析提供了可供选择的程序集,而HttpControllerTypeResolver具体进行类型解析,其均实现了接口IHttpControllerTypeResolver，其只有一个方法GetControllerTypes，而且以IAssembIiesResolver为参数，提供类型程序集。如下：

   public interface IHttpControllerTypeResolver
    {
        //参数IAssembliesResolver提供解析的程序集
        ICollection<Type> GetControllerTypes(IAssembliesResolver assembliesResolver);
    }

　　即根据提供的程序集参数，获取所有符合条件的HttpControllerType列表，现在还没解析完，后续还要从其中选择一个合适的，只是返回可供选择的列表，默认实现是DefaultHttpControllerTypeResolver。

　　注意点：

• 委托 Predicate<Type>，Func<Assembly, Type[]>这种函数式编程用法，把函数当属性和参数
• 只是从多个指定程序集中返回可供选择的HttpControllerType列表，还不是最后解析出的类型
• 判断HttpController类型有效规则，即外部可见 (IsVisibIe=true)的实例 (IsAbstract=false)类 (IsClass=true)，直接或耆间接实现了接口IHttpController，类型名称必须以“Controller” 为后缀,但是不区分大小写 (即 可以使用 “controIler” 作为后缀 )。

public class DefaultHttpControllerTypeResolver : IHttpControllerTypeResolver
    {
        //判断是否为有效Controller的委托，默认指定了IsControllerType，也可以在构造函数指定
        private readonly Predicate<Type> _isControllerTypePredicate;
        //从程序集获取Type[]的委托，可以直接属性设置
        private Func<Assembly, Type[]> _getTypesFunc = GetTypes;
 
        //构造函数，可以指定一个委托来判断是不是控制器类型，默认使用下边的IsControllerType
        public DefaultHttpControllerTypeResolver()
            : this(IsControllerType)
        {
        }
 
        //构造函数，可以指定一个委托来判断是不是控制器类型
        public DefaultHttpControllerTypeResolver(Predicate<Type> predicate)
        {
            if (predicate == null)
            {
                throw Error.ArgumentNull("predicate");
            }
 
            _isControllerTypePredicate = predicate;
        }
 
        //只读，否为有效Controller的委托
        protected internal virtual Predicate<Type> IsControllerTypePredicate
        {
            get { return _isControllerTypePredicate; }
        }
 
        //默认的用来判断是否是控制器的委托predicate
        internal static bool IsControllerType(Type t)
        {
            Contract.Assert(t != null);
            return
                t != null &&
                t.IsClass &&
                t.IsVisible &&
                !t.IsAbstract &&
                typeof(IHttpController).IsAssignableFrom(t) &&
                HasValidControllerName(t);
        }
 
        //返回可用的控制器列表
        public virtual ICollection<Type> GetControllerTypes(IAssembliesResolver assembliesResolver)
        {
            if (assembliesResolver == null)
            {
                throw Error.ArgumentNull("assembliesResolver");
            }
 
            List<Type> result = new List<Type>();
 
            // 从assembliesResolver获取所有程序集
            ICollection<Assembly> assemblies = assembliesResolver.GetAssemblies();
            //遍历每个程序集
            foreach (Assembly assembly in assemblies)
            {
                Type[] exportedTypes = null;
                if (assembly == null || assembly.IsDynamic)
                {
                    // 空或动态程序集就继续下个程序集，不操作当前程序集
                    continue;
                }
 
                try
                {
                    //从程序集中获取Type[]
                    exportedTypes = _getTypesFunc(assembly);
                }
                catch (ReflectionTypeLoadException ex)
                {
                    exportedTypes = ex.Types;
                }
                catch
                {
                    //忽略异常，继续解析，不影响最后结果，除非找不到NOT FOUND
                    continue;
                }
 
                if (exportedTypes != null)
                {
                    //从Type[]中把有效的ControllerType存放到结果列表中
                    result.AddRange(exportedTypes.Where(x => TypeIsVisible(x) && IsControllerTypePredicate(x)));
                }
            }
 
            return result;
        }
 
        //默认使用的从程序集获取Type[]
        internal static Type[] GetTypes(Assembly assembly)
        {
            return assembly.GetTypes();
        }
 
        // 要以Controller结尾，但不能就是Controller，因为路由解析的控制器也不会为空
        internal static bool HasValidControllerName(Type controllerType)
        {
            Contract.Assert(controllerType != null);
            string controllerSuffix = DefaultHttpControllerSelector.ControllerSuffix;
            return controllerType.Name.Length > controllerSuffix.Length && controllerType.Name.EndsWith(controllerSuffix, StringComparison.OrdinalIgnoreCase);
        }
 
        //设置从程序集获取Type[]的委托
        internal void SetGetTypesFunc(Func<Assembly, Type[]> getTypesFunc)
        {
            _getTypesFunc = getTypesFunc;
        }
 
        private static bool TypeIsVisible(Type type)
        {
            //IsVisible是不是可以由程序集代码外访问
            return (type != null && type.IsVisible);
        }
    }

　　

　　其也可以通过ServicesContainer扩展方法直接获取：

　　

3、HttpControllerTypeCache

　　用来缓存反射出来的HttpControllerType，提高性能，是对HttpControllerTypeResolver解析出来的HttpController类型列表的缓存。

　　缓存是一个Dictionary<string, ILookup<string, Type>>字典类型，Key为去除Controller后的部分，不区分大小写，如ProductController，Key为"Producct"，Value为一个 ILookup<string, Type>类型，其Key可以重复，Key为控制器所在的命名空间，如ProductController所在命名空间"MyNameSpace",Value为具体的控制器类型如"ProductController"。

　　注意：

　　相同名称的控制器可能存在不同程序集和不同命名空间下

internal sealed class HttpControllerTypeCache
    {
        private readonly HttpConfiguration _configuration;
        //惰性加载，缓存，Key为控制器名称出去Controller的部分（不区分大小写），
        //Value为一个ILookup<string, Type>，其Key可以重复，为控制所在的命名空间，Value为对应的控制器类型
        //相同名称的控制器可能存在不同程序集和不同命名空间下
        private readonly Lazy<Dictionary<string, ILookup<string, Type>>> _cache;
 
        public HttpControllerTypeCache(HttpConfiguration configuration)
        {
            if (configuration == null)
            {
                throw Error.ArgumentNull("configuration");
            }
 
            _configuration = configuration;
            _cache = new Lazy<Dictionary<string, ILookup<string, Type>>>(InitializeCache);
        }
 
        //由于使用Lazy，调用该属性时候，才调用下边的InitializeCache
        internal Dictionary<string, ILookup<string, Type>> Cache
        {
            get { return _cache.Value; }
        }
 
        //根据控制器名称获取可选的ControllerType列表，从缓存读取
        public ICollection<Type> GetControllerTypes(string controllerName)
        {
            if (String.IsNullOrEmpty(controllerName))
            {
                throw Error.ArgumentNullOrEmpty("controllerName");
            }
 
            HashSet<Type> matchingTypes = new HashSet<Type>();
 
            ILookup<string, Type> namespaceLookup;
            if (_cache.Value.TryGetValue(controllerName, out namespaceLookup))
            {
                foreach (var namespaceGroup in namespaceLookup)
                {
                    matchingTypes.UnionWith(namespaceGroup);
                }
            }
 
            return matchingTypes;
        }
 
        //初始化缓存
        private Dictionary<string, ILookup<string, Type>> InitializeCache()
        {
            //获取AssembliesResolver服务实例
            IAssembliesResolver assembliesResolver = _configuration.Services.GetAssembliesResolver();
            //获取ControllersResolver服务实例
            IHttpControllerTypeResolver controllersResolver = _configuration.Services.GetHttpControllerTypeResolver();
            //调用ControllersResolver.GetControllerTypes以assembliesResolver为参数获取ControllerType列表
            ICollection<Type> controllerTypes = controllersResolver.GetControllerTypes(assembliesResolver);
            //先对解析出来的ControllerType列表按照ControllerType去除Controller后的名称分组，不区分大小写（OrdinalIgnoreCase）
            var groupedByName = controllerTypes.GroupBy(
                t => t.Name.Substring(, t.Name.Length - DefaultHttpControllerSelector.ControllerSuffix.Length),
                StringComparer.OrdinalIgnoreCase);
            //再转换成Dictionary<string, ILookup<string, Type>>缓存结构
            return groupedByName.ToDictionary(
                g => g.Key,
                g => g.ToLookup(t => t.Namespace ?? String.Empty, StringComparer.OrdinalIgnoreCase),
                StringComparer.OrdinalIgnoreCase);
        }
    }

4、IHttpControllerSelector DefaultHttpControllerSelector

　　HttpControllerTypeResolver只是解析出所有合法的ControllerType列表，接下来要根据请求选择出匹配的HttpController类型。

　　通过HttpControllerSelector来完成，其都实现接口IHttpControllerSelector，其主要有两个方法，如下：

 public interface IHttpControllerSelector
    {
        //根据请求选择一个匹配的控制器对应的描述符
        HttpControllerDescriptor SelectController(HttpRequestMessage request);
 
        //返回描述所有HttpController类型的HttpControllerDescriptor对象与对应的HttpController名称之间的映射夫系
        IDictionary<string, HttpControllerDescriptor> GetControllerMapping();
    }

　　同前边，默认实现DefaultHttpControllerSelector，也是是在服务容器里注册的,且同

　　

　　

　　主要逻辑：

• 控制器名称获取，不管Web Host还是Self Host路由解析数据最后都是放在HttpRequestMessage的属性字典中，所以先从请求中获取路由数据，再得到controller名称。如果路由变量中不存在名为controller的数据，或者程序集不存在或存在多个ControllerType，都会抛出异常
• 丢弃在不同命名空间有多个匹配结果的控制器，比如，对于product名称的控制器，在A名称空间和B命名空间都有ProductController，由于系统不知道激活哪一个，所以采用的策略是两个都丢弃。这个逻辑在方法GetControllerMapping()
• 系统会对GetControllerMapping结果缓存，我们在HttpControllerTypeResolver阶段解析出来的ControllerType在不同命名空间中存在多个匹配的控制器，所以采用Dictionary<string, ILookup<string, Type>>缓存，而GetControllerMapping返回的是IDictionary<string, HttpControllerDescriptor>类型，会丢弃上一点中的重复的控制器，返回的都是唯一的结果
• 有两个缓存结构，一个是HttpControllerTypeCache 存放了所有合法的ControllerType，另一个是Lazy<ConcurrentDictionary<string, HttpControllerDescriptor>> _controllerInfoCache，它是根据前者构建出来的
• 编程技巧，使用Lazy，Lazy<ConcurrentDictionary<string, HttpControllerDescriptor>> _controllerInfoCache，在从缓存_controllerInfoCache里读取数据时候，才去构建缓存内容，详细见代码注释

public class DefaultHttpControllerSelector : IHttpControllerSelector
    {
        public static readonly string ControllerSuffix = "Controller";
 
        private const string ControllerKey = "controller";
 
        private readonly HttpConfiguration _configuration;
        //ControllerType缓存
        private readonly HttpControllerTypeCache _controllerTypeCache;
        private readonly Lazy<ConcurrentDictionary<string, HttpControllerDescriptor>> _controllerInfoCache;
 
        public DefaultHttpControllerSelector(HttpConfiguration configuration)
        {
            if (configuration == null)
            {
                throw Error.ArgumentNull("configuration");
            }
            //Lazy惰性加载，用到_controllerInfoCache时候才去执行InitializeControllerInfoCache，进行缓存数据构建
            _controllerInfoCache = new Lazy<ConcurrentDictionary<string, HttpControllerDescriptor>>(InitializeControllerInfoCache);
            _configuration = configuration;
            _controllerTypeCache = new HttpControllerTypeCache(_configuration);
        }
 
        //从请求中匹配指定控制器名称的控制器描述符号，从缓存中读取，缓存构建时机是在读取缓存时候，使用Lazy实现
        public virtual HttpControllerDescriptor SelectController(HttpRequestMessage request)
        {
            if (request == null)
            {
                throw Error.ArgumentNull("request");
            }
 
            IHttpRouteData routeData = request.GetRouteData();
            HttpControllerDescriptor controllerDescriptor;
            if (routeData != null)
            {
                //先按特性路由（以后再说）解析，如果解析出数据，就直接返回
                controllerDescriptor = GetDirectRouteController(routeData);
                if (controllerDescriptor != null)
                {
                    return controllerDescriptor;
                }
            }
            //非特性路由则
            //从HttpRequestMessage属性字典中获取控制器名称，获取不到就NotFound
            string controllerName = GetControllerName(request);
            if (String.IsNullOrEmpty(controllerName))
            {
                throw new HttpResponseException(request.CreateErrorResponse(
                    HttpStatusCode.NotFound,
                    Error.Format(SRResources.ResourceNotFound, request.RequestUri),
                    Error.Format(SRResources.ControllerNameNotFound, request.RequestUri)));
            }
            //从控制器描述符缓存中获取，找到就直接返回，在此Lazy惰性加载，才去执行InitializeControllerInfoCache，进行缓存数据构建
            if (_controllerInfoCache.Value.TryGetValue(controllerName, out controllerDescriptor))
            {
                return controllerDescriptor;
            }
 
            //找不到就根据实际情况，抛出不同异常
            ICollection<Type> matchingTypes = _controllerTypeCache.GetControllerTypes(controllerName);
 
            // ControllerInfoCache is already initialized.
            Contract.Assert(matchingTypes.Count != );
            //根据不同原因创建不同类型异常
            if (matchingTypes.Count == )
            {
                // 没有匹配
                throw new HttpResponseException(request.CreateErrorResponse(
                    HttpStatusCode.NotFound,
                    Error.Format(SRResources.ResourceNotFound, request.RequestUri),
                    Error.Format(SRResources.DefaultControllerFactory_ControllerNameNotFound, controllerName)));
            }
            else
            {
                // 匹配多个类型
                throw CreateAmbiguousControllerException(request.GetRouteData().Route, controllerName, matchingTypes);
            }
        }
 
        public virtual IDictionary<string, HttpControllerDescriptor> GetControllerMapping()
        {
            return _controllerInfoCache.Value.ToDictionary(c => c.Key, c => c.Value, StringComparer.OrdinalIgnoreCase);
        }
 
        //从HttpRequestMessage的属性字典中获取控制器名称
        public virtual string GetControllerName(HttpRequestMessage request)
        {
            if (request == null)
            {
                throw Error.ArgumentNull("request");
            }
            //先从HttpRequestMessage的属性字典中获取路由数据
            IHttpRouteData routeData = request.GetRouteData();
            if (routeData == null)
            {
                return null;
            }
 
            // TryGetValue获取key为controller的路由变量值
            string controllerName = null;
            routeData.Values.TryGetValue(ControllerKey, out controllerName);
            return controllerName;
        }
 
        //特性路由逻辑以后再说
        private static HttpControllerDescriptor GetDirectRouteController(IHttpRouteData routeData)
        {
            CandidateAction[] candidates = routeData.GetDirectRouteCandidates();
            if (candidates != null)
            {
                // Set the controller descriptor for the first action descriptor
                Contract.Assert(candidates.Length > );
                Contract.Assert(candidates[].ActionDescriptor != null);
 
                HttpControllerDescriptor controllerDescriptor = candidates[].ActionDescriptor.ControllerDescriptor;
 
                // Check that all other candidate action descriptors share the same controller descriptor
                for (int i = ; i < candidates.Length; i++)
                {
                    CandidateAction candidate = candidates[i];
                    if (candidate.ActionDescriptor.ControllerDescriptor != controllerDescriptor)
                    {
                        // We've found an ambiguity (multiple controllers matched)
                        throw CreateDirectRouteAmbiguousControllerException(candidates);
                    }
                }
 
                return controllerDescriptor;
            }
 
            return null;
        }
 
        private static Exception CreateDirectRouteAmbiguousControllerException(CandidateAction[] candidates)
        {
            Contract.Assert(candidates != null);
            Contract.Assert(candidates.Length > );
 
            HashSet<Type> matchingTypes = new HashSet<Type>();
            for (int i = ; i < candidates.Length; i++)
            {
                matchingTypes.Add(candidates[i].ActionDescriptor.ControllerDescriptor.ControllerType);
            }
 
            // we need to generate an exception containing all the controller types
            StringBuilder typeList = new StringBuilder();
            foreach (Type matchedType in matchingTypes)
            {
                typeList.AppendLine();
                typeList.Append(matchedType.FullName);
            }
 
            return Error.InvalidOperation(SRResources.DirectRoute_AmbiguousController, typeList, Environment.NewLine);
        }
 
        private static Exception CreateAmbiguousControllerException(IHttpRoute route, string controllerName, ICollection<Type> matchingTypes)
        {
            Contract.Assert(route != null);
            Contract.Assert(controllerName != null);
            Contract.Assert(matchingTypes != null);
 
            // Generate an exception containing all the controller types
            StringBuilder typeList = new StringBuilder();
            foreach (Type matchedType in matchingTypes)
            {
                typeList.AppendLine();
                typeList.Append(matchedType.FullName);
            }
 
            string errorMessage = Error.Format(SRResources.DefaultControllerFactory_ControllerNameAmbiguous_WithRouteTemplate, controllerName, route.RouteTemplate, typeList, Environment.NewLine);
            return new InvalidOperationException(errorMessage);
        }
 
        //初始化构建ConcurrentDictionary<string, HttpControllerDescriptor>缓存，根据Dictionary<string, ILookup<string, Type>>类型 列表缓存
        private ConcurrentDictionary<string, HttpControllerDescriptor> InitializeControllerInfoCache()
        {
            var result = new ConcurrentDictionary<string, HttpControllerDescriptor>(StringComparer.OrdinalIgnoreCase);
            //由于同一控制器名称在不同命名空间中存在多个控制器类型，所以要去掉重复的，用来记录重复的Key
            var duplicateControllers = new HashSet<string>();
            //先从控制器类型列表中缓存中获取控制器类型列表
            Dictionary<string, ILookup<string, Type>> controllerTypeGroups = _controllerTypeCache.Cache;
 
            //遍历
            foreach (KeyValuePair<string, ILookup<string, Type>> controllerTypeGroup in controllerTypeGroups)
            {
                string controllerName = controllerTypeGroup.Key;
 
                foreach (IGrouping<string, Type> controllerTypesGroupedByNs in controllerTypeGroup.Value)
                {
                    foreach (Type controllerType in controllerTypesGroupedByNs)
                    {
                        if (result.Keys.Contains(controllerName))
                        {
                            //有重复就记录在重复集合里，待移除处理
                            duplicateControllers.Add(controllerName);
                            break;
                        }
                        else
                        {
                            //new  HttpControllerDescriptor
                            result.TryAdd(controllerName, new HttpControllerDescriptor(_configuration, controllerName, controllerType));
                        }
                    }
                }
            }
            //去掉有重复的匹配控制器的数据
            foreach (string duplicateController in duplicateControllers)
            {
                HttpControllerDescriptor descriptor;
                result.TryRemove(duplicateController, out descriptor);
            }
 
            return result;
        }
    }

 5、IHttpControllerActivator DefaultHttpControllerActivator

　　通过HttpControllerTypeResolver解析得到请求（controller名称）对应的控制器描述符（HttpControllerDescriptor）后，通过HttpControllerActivator根据控制器描述符最终创建出HttpController实例，其都实现接口IHttpControllerActivator ，其定义如下：

  public interface IHttpControllerActivator
    {
        //根据HttpControllerDescriptor创建出IHttpController
        IHttpController Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType);
    }

　　DefaultHttpControllerActivator是默认实现，其配置同前边几个，不再赘述

　　主要逻辑：

• 在Create方法中，如果dependency resolver可以解析返回，就直接返回，否则就用创建委托activator来执行创建，而创建委托activator可以缓存到本地缓存和controllerDescriptor.Properties cache缓存，由上一篇可以知道，默认的IoC容器是EmptyResolver，所以dependency resolver都是返回空，所以每次都是通过反射创建实例。
• activator通过反射来创建，在第一点中缓存的是创建对象的委托，而不是HttpController实例，其每次都是重新创建，所以对于多个针对相同的HttpControlIer类型的请求来说,最终创建的HttpController实例都是不同的

 public class DefaultHttpControllerActivator : IHttpControllerActivator
    {
        //缓存HttpControllerDescriptor对应的创建委托
        private Tuple<HttpControllerDescriptor, Func<IHttpController>> _fastCache;
        private object _cacheKey = new object();
 
        //核心创建方法，如果dependency resolver可以解析返回，就直接返回，否则就用创建委托activator来执行创建，
        //而创建委托activator可以缓存到本地缓存和controllerDescriptor.Properties cache缓存
        public IHttpController Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)
        {
            if (request == null)
            {
                throw Error.ArgumentNull("request");
            }
 
            if (controllerDescriptor == null)
            {
                throw Error.ArgumentNull("controllerDescriptor");
            }
 
            if (controllerType == null)
            {
                throw Error.ArgumentNull("controllerType");
            }
 
            try
            {
                Func<IHttpController> activator;
 
                //如果没有定义本地快速缓存
                if (_fastCache == null)
                {
                    IHttpController controller = GetInstanceOrActivator(request, controllerType, out activator);
                    if (controller != null)
                    {
                        //这里返回的是dependency resolver中有定义时候，定义的Controller实例
                        return controller;
                    }
                    else
                    {
                        //初始化创建一个本地缓存cacheItem
                        Tuple<HttpControllerDescriptor, Func<IHttpController>> cacheItem = Tuple.Create(controllerDescriptor, activator);
                        Interlocked.CompareExchange(ref _fastCache, cacheItem, null);
                    }
                }
                else if (_fastCache.Item1 == controllerDescriptor)
                {
                    // 如果有定义本地快速缓存，而且匹配controllerDescriptor key就直接返回
                    activator = _fastCache.Item2;
                }
                else
                {
                    // 如果有定义本地快速缓存，没有匹配controllerDescriptor key，就从controllerDescriptor.Properties cache中获取创建委托
                    object value;
                    if (controllerDescriptor.Properties.TryGetValue(_cacheKey, out value))
                    {
                        activator = (Func<IHttpController>)value;
                    }
                    else
                    {
                        IHttpController controller = GetInstanceOrActivator(request, controllerType, out activator);
                        if (controller != null)
                        {
                            //这里返回的是dependency resolver中有定义时候，定义的Controller实例
                            return controller;
                        }
                        else
                        {
                            //添加进HttpControllerDescriptor.Properties cache
                            controllerDescriptor.Properties.TryAdd(_cacheKey, activator);
                        }
                    }
                }
                //执行创建委托，创建实例
                return activator();
            }
            catch (Exception ex)
            {
                throw Error.InvalidOperation(ex, SRResources.DefaultControllerFactory_ErrorCreatingController, controllerType.Name);
            }
        }
 
        // 返回控制器实例如果在dependency resolver得到就直接返回，否则通过反射创建
        private static IHttpController GetInstanceOrActivator(HttpRequestMessage request, Type controllerType, out Func<IHttpController> activator)
        {
            Contract.Assert(request != null);
            Contract.Assert(controllerType != null);
 
            // 如果dependency resolver可以直接返回controller就直接返回使用
            IHttpController instance = (IHttpController)request.GetDependencyScope().GetService(controllerType);
            if (instance != null)
            {
                activator = null;
                return instance;
            }
 
            //如果dependency resolver没有定义，就返回通过反射直接创建的委托
            activator = TypeActivator.Create<IHttpController>(controllerType);
            return null;
        }
    }

 二、自定义扩展组件HttpControllerActivator

　　从前边IHttpControllerActivator那节知道，每次创建实例都是通过反射完成的，因为默认情况下的IoC容器是EmptyResolver，所以dependency resolver都是返回空，根据代码可以知道，都是通过反射来完成，我们可以通过重新实现IHttpControllerActivator，把服务容器里默认定义的DefaultHttpControllerActivator替换掉，替换掉EmptyResolver的方式，上一篇已经说过。

   public class UnityHttpControllerActivator : IHttpControllerActivator
    {
        public IUnityContainer UnityContainer { get; private set; }
 
        public UnityHttpControllerActivator(IUnityContainer unityContainer)
        {
            this.UnityContainer = unityContainer;
        }
 
        public IHttpController Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType)
        {
            return (IHttpController)this.UnityContainer.Resolve(controllerType);
        }
    }

　　注册：

 UnityContainer unityContainer = new UnityContainer();
 GlobalConfiguration.Configuration.Services.Replace(typeof(IHttpControllerActivator),new UnityHttpControllerActivator(unityContainer));