webapi之jsonp调用

public class CorsHandler : DelegatingHandler
{
const string Origin = "Origin"; const string AccessControlRequestMethod = "Access-Control-Request-Method"; const string AccessControlRequestHeaders = "Access-Control-Request-Headers"; const string AccessControlAllowOrigin = "Access-Control-Allow-Origin"; const string AccessControlAllowMethods = "Access-Control-Allow-Methods"; const string AccessControlAllowHeaders = "Access-Control-Allow-Headers";
protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
bool isCorsRequest = request.Headers.Contains(Origin); bool isPreflightRequest = request.Method == HttpMethod.Options; if (isCorsRequest)
{
if (isPreflightRequest)
{
return Task.Factory.StartNew<HttpResponseMessage>(() =>
{
HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
response.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First()); string accessControlRequestMethod = request.Headers.GetValues(AccessControlRequestMethod).FirstOrDefault(); if (accessControlRequestMethod != null)
{
response.Headers.Add(AccessControlAllowMethods, accessControlRequestMethod);
} string requestedHeaders = string.Join(", ", request.Headers.GetValues(AccessControlRequestHeaders)); if (!string.IsNullOrEmpty(requestedHeaders))
{
response.Headers.Add(AccessControlAllowHeaders, requestedHeaders);
} return response;
}, cancellationToken);
}
else
{
return base.SendAsync(request, cancellationToken).ContinueWith<HttpResponseMessage>(t =>
{
HttpResponseMessage resp = t.Result;
resp.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First()); return resp;
});
}
}
else
{
return base.SendAsync(request, cancellationToken);
}
}
}

protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
GlobalConfiguration.Configuration.MessageHandlers.Add(new CorsHandler());
WebApiConfig.Register(GlobalConfiguration.Configuration);
FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
RouteConfig.RegisterRoutes(RouteTable.Routes);
}

public string Get(int id)
{
var callback = HttpContext.Current.Request["callback"];
var u = new User { Name = "AA", Age = id };
var result = new JavaScriptSerializer().Serialize(u);
if (string.IsNullOrWhiteSpace(callback))
return result;
return string.Format("{0}({1})", callback, result);
}

$.ajax({
type: "get",
url: "http://localhost:21931/api/myapi/12311111",
contentType: "application/json;",
success: function (msg) {
jalert(JSON.stringify(msg));
},
error: function (a, b, c) {
jalert("error");
}
});