WebAPI 消息处理器

由上图可以看出消息处理器的使用场合和使用方法。

使用场合：

HttpServer 得到请求时.

public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
config.MessageHandlers.Add(new MessageHandler1());
config.MessageHandlers.Add(new MessageHandler2());

// Other code not shown...
}
}

HttpRoutingDispatcher 根据路由分发地址时.

HttpControllerDispatcher 向控制器发送请求时.

public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
config.Routes.MapHttpRoute(
name: "Route1",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);

config.Routes.MapHttpRoute(
name: "Route2",
routeTemplate: "api2/{controller}/{id}",
defaults: new { id = RouteParameter.Optional },
constraints: null,
handler: new MessageHandler2()  // per-route message handler
);

config.MessageHandlers.Add(new MessageHandler1());  // global message handler
}
}

使用方法：委托的一种特例，可以像一环套一环

实现DelegatingHandler代码：

public class MessageHandler1 : DelegatingHandler
{
protected async override Task<HttpResponseMessage> SendAsync(
HttpRequestMessage request, CancellationToken cancellationToken)
{
Debug.WriteLine("Process request");
// Call the inner handler.
var response = await base.SendAsync(request, cancellationToken);
Debug.WriteLine("Process response");
return response;
}
}

参考地址：http://www.asp.net/web-api/overview/advanced/http-message-handlers