[Web API] Web API 2 深入系列(5) 特性路由

目錄

1. 特性路由注冊

2. 路由解析

    - 生成DataTokens

    - 選擇HttpController

    - 選擇Action

特性路由的目的在於更好的提供restful架構的接口,最近好忙(懶),所以更新速度慢.

特性路由注冊

• [Route(模板)] :定義特性路由模板

  • 普通變量

  a/b/{c}

  • 缺省變量

  a/b/{c=d}

  • 變量約束

  a/b/{c:int:range(10,20)}

  • 通配符

  a/b/{*c:datetime}

[RoutePrefix("api/demo")] :定義路由前綴

路由解析

通過IRoutePrefix/IHttpRouteInfoProvider,我們可以直接注冊路由,映射到具體的Controller和Action.

當調用MapHttpAttributeRoutes方法時,WebAPI會創建1個唯一的RouteCollectionRoute作為IHttpRoute並添加到路由表中.

MapHttpAttributeRoutes方法:

public static void MapHttpAttributeRoutes(HttpConfiguration configuration, IInlineConstraintResolver constraintResolver, IDirectRouteProvider directRouteProvider)
{
    RouteCollectionRoute aggregateRoute = new RouteCollectionRoute();
    configuration.Routes.Add("MS_attributerouteWebApi", (IHttpRoute) aggregateRoute);
    Action<HttpConfiguration> previousInitializer = configuration.Initializer;
    configuration.Initializer = (Action<HttpConfiguration>) (config =>
    {
        previousInitializer(config);
        aggregateRoute.EnsureInitialized((Func<IReadOnlyCollection<IHttpRoute>>) (() =>
        {
            subRoutes = new SubRouteCollection();
            AttributeRoutingMapper.AddRouteEntries(subRoutes, configuration, constraintResolver, directRouteProvider);
            return subRoutes;
        }));
    });
}

RouteCollectionRoute是特性路由的HttpRoute對象,既是一個IHttpRoute對象,又是一個IHttpRoute集合.並且其中核心方法為GetRouteData(IHttpRoute其他接口都返回為null),

internal class RouteCollectionRoute : IHttpRoute, IReadOnlyCollection<IHttpRoute>, IEnumerable<IHttpRoute>, IEnumerable
{
    public IHttpRouteData GetRouteData(string virtualPathRoot, HttpRequestMessage request)
    {
      List<IHttpRouteData> httpRouteDataList = new List<IHttpRouteData>();
      //調用內部的SubRoutes對象
      foreach (IHttpRoute subRoute in (IEnumerable<IHttpRoute>) this.SubRoutes)
      {
        IHttpRouteData routeData = subRoute.GetRouteData(virtualPathRoot, request);
        httpRouteDataList.Add(routeData);
      }
      return (IHttpRouteData) new RouteCollectionRoute.RouteCollectionRouteData((IHttpRoute) this, httpRouteDataList.ToArray());
    }
}

在該方法中,我們發現RouteCollectionRoute調用了內部所有的SubRoutes對象.

而其內部的SubRoutes類型實際為SubRouteCollection類型

internal class SubRouteCollection : IReadOnlyCollection<IHttpRoute>, IEnumerable<IHttpRoute>, IEnumerable
{
    private readonly List<IHttpRoute> _routes = new List<IHttpRoute>();
    private readonly List<RouteEntry> _entries = new List<RouteEntry>();
    public IReadOnlyCollection<RouteEntry> Entries{get;}
}

而SubRoutes的創建是在MapHttpAttributeRoutes方法定義,實際調用是在HttpServer的Send方法初始化的.

protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
    this.EnsureInitialized();
    //...
}

首先驗證一下我們的特性路由注冊位置(定義1個擴展方法)

public static class RouteCollectionExt
{
    public static IEnumerable<IHttpRoute> GetSubRoutes(this HttpRouteCollection routes)
    {
        var route = routes["MS_attributerouteWebApi"];
        var prop = route.GetType().GetProperty("SubRoutes", BindingFlags.Instance | BindingFlags.NonPublic);
        var subRoutes = prop.GetValue(route) as IEnumerable<IHttpRoute>;
        return subRoutes;
    }
}

生成DataTokens

DataTokens這次發揮了一定的作用,同時也告訴我們該如何使用它. (在第1節中,我覺得DataTokens是個冗余設計)

先看下DataTokens上有哪些東西.

private static void ShowSubRoutesTokens(HttpRouteCollection routes)
{
    foreach (var subRoute in routes.GetSubRoutes())
    {
        Console.WriteLine(subRoute.RouteTemplate);
        foreach (var dataToken in subRoute.DataTokens)
        {
            Console.WriteLine("{0,-12}{1}", dataToken.Key, dataToken.Value);
        }
        Console.WriteLine();
    }

}

截圖:

對於DataTokens的actions和precedence的屬性,在DirectRouteBuilder的Build方法中實現

其中actions表示該路由模板對應的actiondescription(在特性路由中,會為每個controller創建獨立的一份子路由.)

而precedence表示匹配的優先級,對於有約束的優先級高於無優先級.(約束分為常量,變量,通配符)

在前2節中,我們講了如何選擇Action以及Controller.
實際上,如果使用特性路由.選擇的機制又有些變化.

選擇HttpController

public virtual HttpControllerDescriptor SelectController(HttpRequestMessage request)
{
    IHttpRouteData routeData = request.GetRouteData();
    if (routeData != null)
    {
        //在GetDirectRouteController內獲取了特性路由對應的Controller,同時要求匹配的所有特性路由對應的Controller為同一個
        HttpControllerDescriptor directRouteController = DefaultHttpControllerSelector.GetDirectRouteController(routeData);
        return directRouteController;
    }
    //普通路由方式
    string controllerName = this.GetControllerName(request);
    //...
}

選擇Action

public HttpActionDescriptor SelectAction(HttpControllerContext controllerContext)
{
    var matchingActions = this.FindMatchingActions(controllerContext, false);
    //...
}

private List<ApiControllerActionSelector.CandidateActionWithParams> FindMatchingActions(HttpControllerContext controllerContext, bool ignoreVerbs = false)
{
    //此處做特性路由判斷
    IEnumerable<IHttpRouteData> subRoutes = controllerContext.RouteData.GetSubRoutes();
    return subRoutes == null ? 普通路由 : 特性路由;
}

備注:
- 如果我們為特性路由指定了Name,則會自動創建一個IHttpRoute綁定到RouteCollection上.(這步是在HttpConfiguration初始化中最后做判斷完成的)

- 文章中的代碼並非完整WebAPI代碼,一般是經過自己精簡后的.

- 本篇內容使用MarkDown語法編輯

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