[Web API] Web API 2 深入系列(5) 特性路由

目录

1. 特性路由注册

2. 路由解析

    - 生成DataTokens

    - 选择HttpController

    - 选择Action

特性路由的目的在于更好的提供restful架构的接口,最近好忙(懒),所以更新速度慢.

特性路由注册

• [Route(模板)] :定义特性路由模板

  • 普通变量

  a/b/{c}

  • 缺省变量

  a/b/{c=d}

  • 变量约束

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

  • 通配符

  a/b/{*c:datetime}

[RoutePrefix("api/demo")] :定义路由前缀

路由解析

通过IRoutePrefix/IHttpRouteInfoProvider,我们可以直接注册路由,映射到具体的Controller和Action.

当调用MapHttpAttributeRoutes方法时,WebAPI会创建1个唯一的RouteCollectionRoute作为IHttpRoute并添加到路由表中.

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对象,既是一个IHttpRoute对象,又是一个IHttpRoute集合.并且其中核心方法为GetRouteData(IHttpRoute其他接口都返回为null),

internal class RouteCollectionRoute : IHttpRoute, IReadOnlyCollection<IHttpRoute>, IEnumerable<IHttpRoute>, IEnumerable
{
    public IHttpRouteData GetRouteData(string virtualPathRoot, HttpRequestMessage request)
    {
      List<IHttpRouteData> httpRouteDataList = new List<IHttpRouteData>();
      //调用内部的SubRoutes对象
      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());
    }
}

在该方法中,我们发现RouteCollectionRoute调用了内部所有的SubRoutes对象.

而其内部的SubRoutes类型实际为SubRouteCollection类型

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的创建是在MapHttpAttributeRoutes方法定义,实际调用是在HttpServer的Send方法初始化的.

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

首先验证一下我们的特性路由注册位置(定义1个扩展方法)

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这次发挥了一定的作用,同时也告诉我们该如何使用它. (在第1节中,我觉得DataTokens是个冗余设计)

先看下DataTokens上有哪些东西.

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();
    }

}

截图:

对于DataTokens的actions和precedence的属性,在DirectRouteBuilder的Build方法中实现

其中actions表示该路由模板对应的actiondescription(在特性路由中,会为每个controller创建独立的一份子路由.)

而precedence表示匹配的优先级,对于有约束的优先级高于无优先级.(约束分为常量,变量,通配符)

在前2节中,我们讲了如何选择Action以及Controller.
实际上,如果使用特性路由.选择的机制又有些变化.

选择HttpController

public virtual HttpControllerDescriptor SelectController(HttpRequestMessage request)
{
    IHttpRouteData routeData = request.GetRouteData();
    if (routeData != null)
    {
        //在GetDirectRouteController内获取了特性路由对应的Controller,同时要求匹配的所有特性路由对应的Controller为同一个
        HttpControllerDescriptor directRouteController = DefaultHttpControllerSelector.GetDirectRouteController(routeData);
        return directRouteController;
    }
    //普通路由方式
    string controllerName = this.GetControllerName(request);
    //...
}

选择Action

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

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

备注:
- 如果我们为特性路由指定了Name,则会自动创建一个IHttpRoute绑定到RouteCollection上.(这步是在HttpConfiguration初始化中最后做判断完成的)

- 文章中的代码并非完整WebAPI代码,一般是经过自己精简后的.

- 本篇内容使用MarkDown语法编辑

首发地址:http://neverc.cnblogs.com/p/5975086.html