在实际的项目中，会存在大量的自定义路由，URL很容易被错误的路由捕获，现在我们就实现一个这样的诊断工具，该工具通过实现一个自定义的IHttpModule来实现。

首先，我们创建CustomRouteHandler：

    public class CustomRouteHandler : IRouteHandler
    {
        public IHttpHandler GetHttpHandler(RequestContext requestContext)
        {
            if(HasQueryStringKey("routeInfo", requestContext.HttpContext.Request))
            {
                OutputRouteDiagnostics(requestContext.RouteData, requestContext.HttpContext);
            }

            var handler = new CustomMvcHandler(requestContext);            
            return handler;
        }

        private bool HasQueryStringKey(string keyToTest, HttpRequestBase request)
        {
            return Regex.IsMatch(request.Url.Query, string.Format(@"^\?{0}$", keyToTest));
        }

        
        private void OutputRouteDiagnostics(RouteData routeData, HttpContextBase context)
        {
            var response = context.Response;
            response.Write(
                @"<style>body {font-family: Arial;}
                         table th {background-color: #359; color: #fff;}
                  </style>
            <h1>Route Data:</h1>
            <table border='1' cellspacing='0' cellpadding='3'>
                <tr><th>Key</th><th>Value</th></tr>");
            foreach (var pair in routeData.Values)
            {
                response.Write(string.Format("<tr><td>{0}</td><td>{1}</td></tr>", pair.Key, pair.Value));
            }
            response.Write(
                @"</table>
                <h1>Routes:</h1>
                <table border='1' cellspacing='0' cellpadding='3'>
                    <tr><th></th><th>Route</th></tr>");

            bool foundRouteUsed = false;
            foreach(Route r in RouteTable.Routes)
            {
                response.Write("<tr><td>");
                bool matches = r.GetRouteData(context) != null;
                string backgroundColor = matches ? "#bfb" : "#fbb";
                if(matches && !foundRouteUsed)
                {
                    response.Write("&raquo;");
                    foundRouteUsed = true;    
                }
                response.Write(string.Format(
                    "</td><td style='font-family: Courier New; background-color:{0}'>{1}</td></tr>",
                    backgroundColor, r.Url));                
            }

            response.End();
        }
    }

CustomRouteHandler中使用到了一个CustomMvcHandler，如下：

    public class CustomMvcHandler : MvcHandler
    {
        public CustomMvcHandler(RequestContext requestContext)
            : base(requestContext)
        {
        }

        protected override void ProcessRequest(HttpContext httpContext)
        {
            try
            {
                base.ProcessRequest(httpContext);
            }
            catch (Exception exc)
            {
                throw new ApplicationException("RouteUsed:" +
                       RequestContext.RouteData.Route.GetVirtualPath(
                        RequestContext, RequestContext.RouteData.Values), exc);
            }
        }
    }

其次，我们需要在MapRoute的时候指定CustomRouteHandler，如下：

            routes.MapRoute(
                "Default", // Route name
                "Home/{action}/{id}", // URL with parameters
                new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
            ).RouteHandler = new CustomRouteHandler();

最终的结果，如果我们想要看当前URL的路由信息，则输入URL如：http://localhost:12205/Home?routeInfo，会显式如下：

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