MVC路由机制（转）

今天我来缕一下MVC的路由机制，因为使用MVC已经快一年了，之前也只是上手，没有系统去理会。项目完了，结合实际使用，回过头来深入一下。

MVC 学习索引(点击即可)

一个请求进入IIS后

传统ASP.NET 路由部分

1、IIS根据文件类型将请求转交给相应的处理程序，如果属于ASP.NET文件，则将请求转发给aspnet_isapi.dll。(注：在II6和IIS7上的处理方式是有区别的)

2、 HTTP处理模块UrlRoutingModule接收到请求后，循环调用其RouteCollection集合中的RouteBase对象，找出匹配的RouteBase。

3、根据匹配的RouteBase对象返回的RoueData对象，获取RouteHandler。

4、RouteHandler返回一个HTTP处理程序(IHttpHandler)，最终通过此处理程序处理请求，生成应答内容。

5.、如果RouteHandler为MvcRouteHandler，并且其返回的HTTP处理程序为MvcHandler，则进入到MVC框架，MvcHandler对象负责调用适当的控制器和活动方法，生成应答内容。

MVC 路由部分　

关键类说明

１、UrlRoutingModule类

此类事路由系统的核心类，其主要功能是根据请求上下文找出合适的RouteBase对象。属性RouteCollection是一个RouteBase对象集合，UrlRoutingModule接收到请求后，循环RouteCollection集合中的RouteBase对象，调用其GetRouteData方法，如果该方法返回的RouteData对象不为null，则终止循环，将RouteData对象存入RequestContext。然后根据RouteData的RouteHandler获取合适的IHttpHandler处理程序。

UrlRoutingModule实际上是一个ASP.NET的HTTP 处理模块，所以它通过配置文件的<httpMoudles>配置节点来添加的。

2、RouteTable类

用于存储应用程序的路由集合，静态属性Routes返回应用程序的路由集合，它实际等同于UrlRoutingModule的RouteCollection属性。通过RouteTable.Routes.Add方法可以添加自定义的RouteBase对象。

3、RouteBase类

表示一个ASP.NET路由的基类[System.Web.Routing]，所有的路由都应该继承自此类。

GetRouteData方法检查传入的HttpContextBase信息是否符合路由规则，符合则返回一个RouteData对象，不符合则返回null，此方法由UrlRoutingModule类在循环RouteTable.Routes集合时调用。

GetVirtualPath方法根据路由数据生成相应的Url。

4、Route类

是RouteBase的一个实现，主要添加了几个属性：

Constraints：对URL的约束条件

DataTokens：传递到路由处理程序的自定义值

Defaults：Url不包含指定参数时得默认值

RouteHandler：一个路由处理程序(IRouteHandler)

5、IRouteHandler接口

路由处理程序接口，包含一个GetHttpHandler方法，用于返回一个IHttpHandler处理程序对象。

6、MvcRouteHandler类

Mvc框架实现的一个路由处理程序，其GetHttpHandler方法返回一个MvcHandler对象

#region IRouteHandler Members
IHttpHandler IRouteHandler.GetHttpHandler(RequestContext requestContext) {
return GetHttpHandler(requestContext);
}
#endregion

7、MvcHandler

由MvcRouteHandler返回，根据请求信息，调用合适的控制器和方法，生成应答内容。

public class MvcHandler : IHttpAsyncHandler, IHttpHandler, IRequiresSessionState {
private static readonly object _processRequestTag = new object();
private ControllerBuilder _controllerBuilder;
internal static readonly string MvcVersion = GetMvcVersionString();
public static readonly string MvcVersionHeaderName = "X-AspNetMvc-Version";
public MvcHandler(RequestContext requestContext) {
if (requestContext == null) {
throw new ArgumentNullException("requestContext");
}
RequestContext = requestContext;
}
internal ControllerBuilder ControllerBuilder {
get {
if (_controllerBuilder == null) {
_controllerBuilder = ControllerBuilder.Current;
}
return _controllerBuilder;
}
set {
_controllerBuilder = value;
}
}
public static bool DisableMvcResponseHeader {
get;
set;
}
protected virtual bool IsReusable {
get {
return false;
}
}
public RequestContext RequestContext {
get;
private set;
}
protected internal virtual void AddVersionHeader(HttpContextBase httpContext) {
if (!DisableMvcResponseHeader) {
httpContext.Response.AppendHeader(MvcVersionHeaderName, MvcVersion);
}
}
protected virtual IAsyncResult BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, object state) {
HttpContextBase iHttpContext = new HttpContextWrapper(httpContext);
return BeginProcessRequest(iHttpContext, callback, state);
}
protected internal virtual IAsyncResult BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, object state) {
return SecurityUtil.ProcessInApplicationTrust(() => {
IController controller;
IControllerFactory factory;
ProcessRequestInit(httpContext, out controller, out factory);
IAsyncController asyncController = controller as IAsyncController;
if (asyncController != null) {
// asynchronous controller
BeginInvokeDelegate beginDelegate = delegate(AsyncCallback asyncCallback, object asyncState) {
try {
return asyncController.BeginExecute(RequestContext, asyncCallback, asyncState);
}
catch {
factory.ReleaseController(asyncController);
throw;
}
};
EndInvokeDelegate endDelegate = delegate(IAsyncResult asyncResult) {
try {
asyncController.EndExecute(asyncResult);
}
finally {
factory.ReleaseController(asyncController);
}
};
SynchronizationContext syncContext = SynchronizationContextUtil.GetSynchronizationContext();
AsyncCallback newCallback = AsyncUtil.WrapCallbackForSynchronizedExecution(callback, syncContext);
return AsyncResultWrapper.Begin(newCallback, state, beginDelegate, endDelegate, _processRequestTag);
}
else {
// synchronous controller
Action action = delegate {
try {
controller.Execute(RequestContext);
}
finally {
factory.ReleaseController(controller);
}
};
return AsyncResultWrapper.BeginSynchronous(callback, state, action, _processRequestTag);
}
});
}
protected internal virtual void EndProcessRequest(IAsyncResult asyncResult) {
SecurityUtil.ProcessInApplicationTrust(() => {
AsyncResultWrapper.End(asyncResult, _processRequestTag);
});
}
private static string GetMvcVersionString() {
// DevDiv 216459:
// This code originally used Assembly.GetName(), but that requires FileIOPermission, which isn't granted in
// medium trust. However, Assembly.FullName *is* accessible in medium trust.
return new AssemblyName(typeof(MvcHandler).Assembly.FullName).Version.ToString(2);
}
protected virtual void ProcessRequest(HttpContext httpContext) {
HttpContextBase iHttpContext = new HttpContextWrapper(httpContext);
ProcessRequest(iHttpContext);
}
protected internal virtual void ProcessRequest(HttpContextBase httpContext) {
SecurityUtil.ProcessInApplicationTrust(() => {
IController controller;
IControllerFactory factory;
ProcessRequestInit(httpContext, out controller, out factory);
try {
controller.Execute(RequestContext);
}
finally {
factory.ReleaseController(controller);
}
});
}
private void ProcessRequestInit(HttpContextBase httpContext, out IController controller, out IControllerFactory factory) {
// If request validation has already been enabled, make it lazy. This allows attributes like [HttpPost] (which looks
// at Request.Form) to work correctly without triggering full validation.
bool? isRequestValidationEnabled = ValidationUtility.IsValidationEnabled(HttpContext.Current);
if (isRequestValidationEnabled == true) {
ValidationUtility.EnableDynamicValidation(HttpContext.Current);
}
AddVersionHeader(httpContext);
RemoveOptionalRoutingParameters();
// Get the controller type
string controllerName = RequestContext.RouteData.GetRequiredString("controller");
// Instantiate the controller and call Execute
factory = ControllerBuilder.GetControllerFactory();
controller = factory.CreateController(RequestContext, controllerName);
if (controller == null) {
throw new InvalidOperationException(
String.Format(
CultureInfo.CurrentCulture,
MvcResources.ControllerBuilder_FactoryReturnedNull,
factory.GetType(),
controllerName));
}
}
private void RemoveOptionalRoutingParameters() {
RouteValueDictionary rvd = RequestContext.RouteData.Values;
// Get all keys for which the corresponding value is 'Optional'.
// ToArray() necessary so that we don't manipulate the dictionary while enumerating.
string[] matchingKeys = (from entry in rvd
where entry.Value == UrlParameter.Optional
select entry.Key).ToArray();
foreach (string key in matchingKeys) {
rvd.Remove(key);
}
}
#region IHttpHandler Members
bool IHttpHandler.IsReusable {
get {
return IsReusable;
}
}
void IHttpHandler.ProcessRequest(HttpContext httpContext) {
ProcessRequest(httpContext);
}
#endregion
#region IHttpAsyncHandler Members
IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData) {
return BeginProcessRequest(context, cb, extraData);
}
void IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) {
EndProcessRequest(result);
}
#endregion
}

值得一提的是，在MVC3中已经实现异步处理(IHttpAsyncHandler)

8、StopRoutingHandler类

表示一个“不处理URL的路由处理类”，比如MVC在RouteCollection类型上扩展了一个IgnoreRoute方法，用于指示路由系统忽略处理指定的url。其实现方式是生成一个Route对象，指定其RouteHandler属性为一个StopRoutingHandler对象。

9、IRouteConstraint接口

用于构建Route.Constraints属性，表示一个约束条件。Match方法用于检查url是否符合路由规则，符合返回true，否则false。