ASP.NET 学习小记 -- “迷你”MVC实现(1)

ASP.NET 由于采用了管道式设计，具有很好的扩展性。整个ASP.NET MVC应用框架就是通过扩展ASP.NET实现的。通过ASP.NET的管道设计，我们知道，ASP.NET的扩展点主要是体现在HttpModule和HttpHandler这两个核心组件之上，实际上整个ASP.NET MVC的框架就是通过自定义的HttoModule和HttpHandler建立起来的。

当然，要从整体上把握ASP.NET MVC 的工作机制，我们可以通过查看其源码或自己实现一个“迷你版”的ASP.NET MVC 来了解其运行原理。

RouteData

ASP.NET定义了一个全局的路由表，路由表中的每个路由对象报刊一个URL模板。目标Controller和Action的名称可以通过路由变量以占位符（比如“{controller}”和“{action}”）定义在URL模板中，也可以作为路有对象的默认值。对于每一个抵达的HTTP请求，ASP.NET MVC会便利路由表找到一个具有与当前请求URL模式相匹配的路由对象，并最终解析出以Controller和Action名称为核心的路由数据。

   1:      public class RouteData

   2:      {

   3:          /// <summary>

   4:          /// 变量列表

   5:          /// </summary>

   6:          public IDictionary<string, object> Values { get; private set; }

   7:   

   8:          /// <summary>

   9:          /// 其他来源的变量列表

  10:          /// </summary>

  11:          public IDictionary<string, object> DataTokens { get; private set; }

  12:   

  13:          public IRouteHandler RouteHandler { get; set; }

  14:   

  15:          public RouteBase Route { get; set; }

  16:   

  17:          public RouteData()

  18:          {

  19:              this.Values = new Dictionary<string, object>();

  20:              this.DataTokens = new Dictionary<string, object>();

  21:              this.DataTokens.Add("namespaces", new List<string>());

  22:          }

  23:   

  24:          /// <summary>

  25:          /// 获取控制器名称

  26:          /// </summary>

  27:          public string Controller

  28:          {

  29:              get

  30:              {

  31:                  object controllerName = string.Empty;

  32:                  this.Values.TryGetValue("controller", out controllerName);

  33:                  return controllerName.ToString();

  34:              }

  35:          }

  36:   

  37:          /// <summary>

  38:          /// 获取方法名称

  39:          /// </summary>

  40:          public string ActionName

  41:          {

  42:              get

  43:              {

  44:                  object actionName = string.Empty;

  45:                  this.Values.TryGetValue("action", out actionName);

  46:                  return actionName.ToString();

  47:              }

  48:          }

  49:      }

RouteData的RouteHandler属性类型为IRouteHandler接口，该接口具有一个GetHttpHandler方法，用于返回真正用于处理HTTP请求的HttpHandler对象。

   1:      public interface IRouteHandler

   2:      {

   3:          IHttpHandler GetHttpHandler(RequestContext requestContext);

   4:      }

IRouteHandler接口的GetHttpHandler方法接受一个类型为RequestContext的参数，RequestContext表示当前HTTP请求的上下文，其核心就是对当前HttpContext和RouteData的封装。

   1:      public class RequestContext

   2:      {

   3:          public virtual HttpContextBase HttpContext { get; set; }

   4:   

   5:          public virtual RouteData RouteData { get; set; }

   6:      }

Route和RouteTable

RouteData具有一个类型为RouteBase的Route属性，该属性表示生成路由数据对应的路由对象。RouteBase是一个抽象类，它包含一个GetRouteData的方法，该方法用于判断是否与当前请求相匹配。并在匹配的情况下返回用于封装路由数据的RoutData对象。该方法接受一个表示当前HTTP上下文的HttpContextBase对象，如果与当前请求不匹配，则返回null。

   1:      public abstract class RouteBase

   2:      {

   3:          public abstract RouteData GetRouteData(HttpContextBase httpContext);

   4:      }

ASP.NET MVC 提供的基于URL模板的路由机制是通过其子类Route实现的。

   1:      public class Route : RouteBase

   2:      {

   3:   

   4:          public IRouteHandler RouteHandler { get; set; }

   5:   

   6:          public string Url { get; set; }

   7:   

   8:          public IDictionary<string, object> DataTokens { get; set; }

   9:   

  10:          public Route()

  11:          {

  12:              this.DataTokens = new Dictionary<string, object>();

  13:              this.RouteHandler = new MvcRouteHandler();

  14:          }

  15:   

  16:          public override RouteData GetRouteData(System.Web.HttpContextBase httpContext)

  17:          {

  18:              IDictionary<string, object> variables;

  19:              if(this.Match(httpContext.Request.AppRelativeCurrentExecutionFilePath.Substring(2),out variables))

  20:              {

  21:                  RouteData routeData = new RouteData();

  22:                  foreach (var item in variables)

  23:                  {

  24:                      routeData.Values.Add(item.Key, item.Value);

  25:                  }

  26:                  routeData.RouteHandler = this.RouteHandler;

  27:                  return routeData;

  28:              }

  29:              return null;

  30:          }

  31:   

  32:          public bool Match(string requestUrl, out IDictionary<string, object> variables)

  33:          {

  34:              variables = new Dictionary<string, object>();

  35:              string[] strArray1 = requestUrl.Split('/');

  36:              string[] strArray2 = this.Url.Split('/');

  37:              if (strArray1.Length != strArray2.Length)

  38:              {

  39:                  return false;

  40:              }

  41:              for (int i = 0; i < strArray2.Length; i++)

  42:              {

  43:                  if (strArray2[i].StartsWith("{") && strArray2[i].EndsWith("}"))

  44:                  {

  45:                      variables.Add(strArray2[i].Trim("{}".ToCharArray()), strArray1[i]);

  46:                  }

  47:                  else

  48:                  {

  49:                      if(string.Compare(strArray1[i],strArray2[i],true)!=0)

  50:                      {

  51:                          return false;

  52:                      }

  53:                  }

  54:              }

  55:              return true;

  56:          }

  57:      }

由于同一个Web应用可以采用多种不同的URL模式，所欲需要注册多个继承自RouteBase的路由对象，多个路由对象组成一个路由表。

   1:      public class RouteTable

   2:      {

   3:          public static RouteDictionary Routes { get; private set; }

   4:   

   5:          static RouteTable()

   6:          {

   7:              Routes = new RouteDictionary();

   8:          },

   9:      }

RouteDictionary表示一个具名的路由对象列表。这里我们让它继承自Dictionary<string,RouteBase>，其中key表示路由对象的注册名称。在System.Web.Routing中，它实际上是继承自RouteCollection对象。

   1:      public class RouteDictionary:Dictionary<string,RouteBase>

   2:      {

   3:          public RouteData GetRouteData(HttpContextBase httpContext)

   4:          {

   5:              foreach (var route in this.Values)

   6:              {

   7:                  RouteData routeData = route.GetRouteData(httpContext);

   8:                  if (routeData != null)

   9:                  {

  10:                      return routeData;

  11:                  }

  12:              }

  13:              return null;

  14:          }

  15:      }

UrlRoutingModule

路由表的作用是对当前的HTTP请求的URL进行解析，从而获取一个以Controller和Action名称为核心的路由数据，即上面介绍的RouteData对象。整个解析过程是通过一个类型为UrlRoutingModule的自定义HttpModule来完成的。

   1:      public class UrlRoutingModule:IHttpModule

   2:      {

   3:          public void Dispose()

   4:          {

   5:              

   6:          }

   7:   

   8:          public void Init(HttpApplication context)

   9:          {

  10:              context.PostResolveRequestCache += OnPostResolveRequestCache;

  11:          }

  12:   

  13:          protected virtual void OnPostResolveRequestCache(object sender, EventArgs e)

  14:          {

  15:              HttpContextWrapper httpContext = new HttpContextWrapper(HttpContext.Current);

  16:              RouteData routeData = RouteTable.Routes.GetRouteData(httpContext);

  17:              if (routeData == null)

  18:              {

  19:                  return;

  20:              }

  21:              RequestContext requestContext = new RequestContext

  22:              {

  23:                  RouteData = routeData,

  24:                  HttpContext = httpContext

  25:              };

  26:              IHttpHandler handler = routeData.RouteHandler.GetHttpHandler(requestContext);

  27:              httpContext.RemapHandler(handler);

  28:          }

  29:      }

当PostResolveRequestCache事件触发之后，UrlRoutingModule通过RouteTable的静态子都属性Routes得到表示全局路由表的RouteDictionary对象，然后调用其GetRouteData方法并传入用于封装当前HttpContext的HttpContextWrapper对象，最终得到一个封装路由数据的RouteData对象。然后根据该对象和之前得到的HttpContextWrapper对象创建一个表示当前请求上下文的RequestContext对象并将其作为参数传入RouteData和RouteHandler的GetHttpHandler方法中，得到一个HttpContext对象，最后我们调用HttpContextWrapper对象的RemapHandler将Handler重新映射，使之用于对当前HTTP请求进行处理。

本学习内容和代码来自《ASP.NET MVC 4 框架揭秘》