为ASP.NET MVC及WebApi添加路由优先级

一、为什么需要路由优先级

大家都知道我们在Asp.Net MVC项目或WebApi项目中注册路由是没有优先级的，当项目比较大、或有多个区域、或多个Web项目、或采用插件式框架开发时，我们的路由注册很可能 不是写在一个文件中的，而是分散在很多不同项目的文件中，这样一来，路由的优先级的问题就突显出来了。

比如： App_Start/RouteConfig.cs中

routes.MapRoute( 
  name: "Default", 
  url: "{controller}/{action}/{id}", 
  defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional } 
); 
 
Areas/Admin/AdminAreaRegistration.cs中 
 
context.MapRoute( 
  name: "Login",  
  url: "login", 
  defaults: new { area = "Admin", controller = "Account", action = "Login", id = UrlParameter.Optional }, 
  namespaces: new string[] { "Wenku.Admin.Controllers" } 
); 

假如是先注册上面那个通用的default路由，再注册这个login的路由，那么无论怎么样，都会先匹配第一个满足条件的路由，也就是第两个路由注册是无效的。
造成这个问题的原因就是这两个路由注册的顺序问题，而Asp.Net MVC及WebApi中注册路由都没有优先级这个概念，所以今天我们就是要自己实现这个想法，在注册路由时加入一个优先级的概念。

二、解决思路

1、先分析路由注册的入口，比如我们新建一个mvc4.0的项目

public class MvcApplication : System.Web.HttpApplication 
{ 
  protected void Application_Start() 
  { 
    AreaRegistration.RegisterAllAreas(); 
 
    WebApiConfig.Register(GlobalConfiguration.Configuration); 
    FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters); 
    RouteConfig.RegisterRoutes(RouteTable.Routes); 
  } 
} 

Mvc路由的注册入口有两个：
a. AreaRegistration.RegisterAllAreas();                                    注册区域路由
b. RouteConfig.RegisterRoutes(RouteTable.Routes);          注册项目路由

WebApi路由注册入口有一个：
WebApiConfig.Register(GlobalConfiguration.Configuration);  注册WebApi路由

2、注册路由的处理类分析

AreaRegistrationContext
RouteCollection
HttpRouteCollection

注册路由时主要是由这三个类来注册处理路由的。

3、路由优先级方案

a、更改路由的注册入口
b、自定义一个路由的结构类RoutePriority及HttpRoutePriority，这两个类下面都有Priority这个属性
c、自定一个RegistrationContext来注册路由，注册的对象为上述自定义路由。
d、所有的路由注册完成之后再按优先顺序添加到RouteCollection及HttpRouteCollection中实际生效。

三、具体实现

1、路由定义

public class RoutePriority : Route 
{ 
  public string Name { get; set; } 
  public int Priority { get; set; } 
 
  public RoutePriority(string url, IRouteHandler routeHandler) 
    : base(url,routeHandler) 
  { 
 
  } 
} 
 
public class HttpRoutePriority 
{ 
  public string Name { get; set; } 
  public int Priority { get; set; } 
  public string RouteTemplate{get;set;} 
  public object Defaults{get;set;} 
  public object Constraints{get;set;} 
  public HttpMessageHandler Handler{get;set;} 
} 

2、定义路由注册的接口

public interface IRouteRegister 
{ 
  void Register(RegistrationContext context); 
} 

3、定义路由注册上下文类

public class RegistrationContext 
{ 
  #region mvc 
  public List<RoutePriority> Routes = new List<RoutePriority>(); 
 
  public RoutePriority MapRoute(string name, string url,int priority=0) 
  { 
    return MapRoute(name, url, (object)null /* defaults */, priority); 
  } 
 
  public RoutePriority MapRoute(string name, string url, object defaults, int priority = 0) 
  { 
    return MapRoute(name, url, defaults, (object)null /* constraints */, priority); 
  } 
 
  public RoutePriority MapRoute(string name, string url, object defaults, object constraints, int priority = 0) 
  { 
    return MapRoute(name, url, defaults, constraints, null /* namespaces */, priority); 
  } 
 
  public RoutePriority MapRoute(string name, string url, string[] namespaces, int priority = 0) 
  { 
    return MapRoute(name, url, (object)null /* defaults */, namespaces, priority); 
  } 
 
  public RoutePriority MapRoute(string name, string url, object defaults, string[] namespaces,int priority=0) 
  { 
    return MapRoute(name, url, defaults, null /* constraints */, namespaces, priority); 
  } 
 
  public RoutePriority MapRoute(string name, string url, object defaults, object constraints, string[] namespaces, int priority = 0) 
  { 
    var route = MapPriorityRoute(name, url, defaults, constraints, namespaces, priority); 
    var areaName = GetAreaName(defaults); 
    route.DataTokens["area"] = areaName; 
 
    // disabling the namespace lookup fallback mechanism keeps this areas from accidentally picking up 
    // controllers belonging to other areas 
    bool useNamespaceFallback = (namespaces == null || namespaces.Length == 0); 
    route.DataTokens["UseNamespaceFallback"] = useNamespaceFallback; 
 
    return route; 
  } 
 
  private static string GetAreaName(object defaults) 
  { 
    if (defaults != null) 
    { 
      var property = defaults.GetType().GetProperty("area"); 
      if (property != null) 
        return (string)property.GetValue(defaults, null); 
    } 
 
    return null; 
  } 
 
  private RoutePriority MapPriorityRoute(string name, string url, object defaults, object constraints, string[] namespaces,int priority) 
  { 
    if (url == null) 
    { 
      throw new ArgumentNullException("url"); 
    } 
 
    var route = new RoutePriority(url, new MvcRouteHandler()) 
    { 
      Name = name, 
      Priority = priority, 
      Defaults = CreateRouteValueDictionary(defaults), 
      Constraints = CreateRouteValueDictionary(constraints), 
      DataTokens = new RouteValueDictionary() 
    }; 
 
    if ((namespaces != null) && (namespaces.Length > 0)) 
    { 
      route.DataTokens["Namespaces"] = namespaces; 
    } 
 
    Routes.Add(route); 
    return route; 
  } 
 
  private static RouteValueDictionary CreateRouteValueDictionary(object values) 
  { 
    var dictionary = values as IDictionary<string, object>; 
    if (dictionary != null) 
    { 
      return new RouteValueDictionary(dictionary); 
    } 
 
    return new RouteValueDictionary(values); 
  } 
  #endregion 
 
  #region http 
  public List<HttpRoutePriority> HttpRoutes = new List<HttpRoutePriority>(); 
 
  public HttpRoutePriority MapHttpRoute(string name, string routeTemplate, int priority = 0) 
  { 
    return MapHttpRoute(name, routeTemplate, defaults: null, constraints: null, handler: null, priority: priority); 
  } 
 
  public HttpRoutePriority MapHttpRoute(string name, string routeTemplate, object defaults, int priority = 0) 
  { 
    return MapHttpRoute(name, routeTemplate, defaults, constraints: null, handler: null, priority: priority); 
  } 
 
  public HttpRoutePriority MapHttpRoute(string name, string routeTemplate, object defaults, object constraints, int priority = 0) 
  { 
    return MapHttpRoute(name, routeTemplate, defaults, constraints, handler: null, priority: priority); 
  } 
 
  public HttpRoutePriority MapHttpRoute(string