WebAPI增加Area以支持无限层级同名Controller

微软的WebAPI默认实现逻辑

默认实现中不支持同名Controller，否则在访问时会报HttpError，在网上找到了各种路由自实现，如

给ASP.net Web API的Controller分类

搭建MVC及WebAPI项目框架时碰到的问题集合

在上述地址的帮助下，根据需求，重新编写了AreaHttpControllerSelector，路由原理与上述地址大同小异，均是通过路由匹配拼接FullName，然后匹配最接近的ApiController，而所谓的最接近，就是指如果根据拼接的Name获取到了多个匹配项，则获取命名空间节点数最少的那个ApiController，以保证在多次注册路由规则时，能够按照从繁到简的方式匹配出相应的Controller（需要注意的是AreaHttpControllerSelector是以controller作为结束分割点的），举例如下

假定注册了以下路由匹配规则（controller、action均为WebAPI的路由占用字符）

           config.Routes.MapHttpRoute(
                name: "DefaultAreaApi",
                routeTemplate: "api/{area}/{controller}/{action}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{action}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );

在Controller目录下存在多层同名且不同层级的Controller，如：

Controller/Area/SameController，对应的命名空间为Controller.Area.SameController
Controller/SameController，对应的命名空间为Controller.SameController

通过api/Area/Same/Get将匹配到Controller/Area/SameController
通过api/Same/Get将匹配到Controller/SameController

相比于参考网址，重新编写的AreaHttpControllerSelector可以支持无限层级的区域，只要命名空间支持，比如

"api/{area1}/{area1}/{area2}/{area3}/{controller}/{action}/{id}"

以下是具体的AreaHttpControllerSelector代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Web;
using System.Web.Http.Dispatcher;
using System.Net.Http;
using System.Web.Http;
using System.Web.Http.Controllers;
using System.Net;

namespace WebAPI
{
    /// <summary>
    /// Represents a area System.Web.Http.Dispatcher.IHttpControllerSelector instance
    /// </summary>
    public class AreaHttpControllerSelector : DefaultHttpControllerSelector
    {
        private readonly HttpConfiguration _configuration;
        /// <summary>
        /// Lazy 当前程序集中包含的所有IHttpController反射集合，TKey为小写的Controller
        /// </summary>
        private readonly Lazy<ILookup<string, Type>> _apiControllerTypes;
        private ILookup<string, Type> ApiControllerTypes
        {
            get
            {
                return this._apiControllerTypes.Value;
            }
        }
        /// <summary>
        /// Initializes a new instance of the AreaHttpControllerSelector class
        /// </summary>
        /// <param name="configuration"></param>
        public AreaHttpControllerSelector(HttpConfiguration configuration)
            : base(configuration)
        {
            this._configuration = configuration;
            this._apiControllerTypes = new Lazy<ILookup<string, Type>>(this.GetApiControllerTypes);
        }
        /// <summary>
        /// 获取当前程序集中 IHttpController反射集合
        /// </summary>
        /// <returns></returns>
        private ILookup<string, Type> GetApiControllerTypes()
        {
            IAssembliesResolver assembliesResolver = this._configuration.Services.GetAssembliesResolver();
            return this._configuration.Services.GetHttpControllerTypeResolver()
                .GetControllerTypes(assembliesResolver)
                .ToLookup(t => t.Name.ToLower().Substring(0, t.Name.Length - DefaultHttpControllerSelector.ControllerSuffix.Length), t => t);
        }
        /// <summary>
        /// Selects a System.Web.Http.Controllers.HttpControllerDescriptor for the given System.Net.Http.HttpRequestMessage.
        /// </summary>
        /// <param name="request"></param>
        /// <returns></returns>
        public override HttpControllerDescriptor SelectController(HttpRequestMessage request)
        {
            HttpControllerDescriptor des = null;
            string controllerName = this.GetControllerName(request);
            if (!string.IsNullOrWhiteSpace(controllerName))
            {
                var groups = this.ApiControllerTypes[controllerName.ToLower()];
                if (groups != null && groups.Any())
                {
                    string endString;
                    var routeDic = request.GetRouteData().Values;//存在controllerName的话必定能取到IHttpRouteData
                    if (routeDic.Count > 1)
                    {
                        StringBuilder tmp = new StringBuilder();
                        foreach (var key in routeDic.Keys)
                        {
                            tmp.Append('.');
                            tmp.Append(routeDic[key]);
                            if (key.Equals(DefaultHttpControllerSelector.ControllerSuffix, StringComparison.CurrentCultureIgnoreCase))
                            {//如果是control，则代表命名空间结束
                                break;
                            }
                        }
                        tmp.Append(DefaultHttpControllerSelector.ControllerSuffix);
                        endString = tmp.ToString();
                    }
                    else
                    {
                        endString = string.Format(".{0}{1}", controllerName, DefaultHttpControllerSelector.ControllerSuffix);
                    }
                    //取NameSpace节点数最少的Type
                    var type = groups.Where(t => t.FullName.EndsWith(endString, StringComparison.CurrentCultureIgnoreCase))
                        .OrderBy(t => t.FullName.Count(s => s == '.')).FirstOrDefault();//默认返回命名空间节点数最少的第一项
                    if (type != null)
                    {
                        des = new HttpControllerDescriptor(this._configuration, controllerName, type);
                    }
                }
            }
            if (des == null)
            {
                throw new HttpResponseException(request.CreateErrorResponse(HttpStatusCode.NotFound,
                    string.Format("No route providing a controller name was found to match request URI '{0}'", request.RequestUri)));
            }
            return des;
        }
    }
}

而用法就是在Global文件的Application_Start方法中替换注册

GlobalConfiguration.Configuration.Services.Replace(typeof(IHttpControllerSelector),
                                                   new AreaHttpControllerSelector(
                                                       GlobalConfiguration.Configuration));