ASP.NET Web API 自定义MediaType实现jsonp跨域调用

　　代码来自《ASP.NET Web API 2 框架揭秘》一书。

　　直接上代码：

　　

/// <summary>
/// 自定义jsonp MediaType
/// </summary>
public class JsonpMediaTypeFormatter : JsonMediaTypeFormatter
{
//callback参数
public string Callback { get; private set; }
public JsonpMediaTypeFormatter(string callback = null)
{
this.Callback = callback;
}

public override Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext)
{
//如果callback不存在，直接调用父类方法
if (string.IsNullOrEmpty(this.Callback))
{
return base.WriteToStreamAsync(type, value, writeStream, content, transportContext);
}
try
{
//否则调用重写的方法
this.WriteToStream(type, value, writeStream, content);
return Task.FromResult<AsyncVoid>(new AsyncVoid());
}
catch(Exception ex)
{
TaskCompletionSource<AsyncVoid> source = new TaskCompletionSource<AsyncVoid>();
source.SetException(ex);
return source.Task;
}
}

private void WriteToStream(Type type, object value, Stream writeStream, HttpContent content)
{
JsonSerializer serializer = JsonSerializer.Create(this.SerializerSettings);
using (StreamWriter writer = new StreamWriter(writeStream,this.SupportedEncodings.First())) {
using (JsonTextWriter jsonTextWriter = new JsonTextWriter(writer) { CloseOutput = false }) {
//添加callback(json)
jsonTextWriter.WriteRaw(this.Callback + "(");
serializer.Serialize(jsonTextWriter, value);
jsonTextWriter.WriteRaw(")");
}
}
}

public override MediaTypeFormatter GetPerRequestFormatterInstance(Type type, HttpRequestMessage request, MediaTypeHeaderValue mediaType)
{

if (request.Method != HttpMethod.Get) { return this; }
string callback;
if (request.GetQueryNameValuePairs().ToDictionary(p => p.Key, p => p.Value).TryGetValue("callback", out callback)) {
return new JsonpMediaTypeFormatter(callback);
}
return this;
}

[StructLayout(LayoutKind.Sequential, Size = 1)]
private struct AsyncVoid { }
}

　　然后在Global.asax中将JsonpMediaTypeFormatter加入

　　

protected void Application_Start()
{
//加入jsonpMediaTypeFormatter
GlobalConfiguration.Configuration.Formatters.Insert(0, new JsonpMediaTypeFormatter());
AreaRegistration.RegisterAllAreas();

GlobalConfiguration.Configure(WebApiConfig.Register);
FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
RouteConfig.RegisterRoutes(RouteTable.Routes);
BundleConfig.RegisterBundles(BundleTable.Bundles);
}

　　Demo演示：

　　我在localhost:55950 用jquery 调用api（http://localhost:55599/api/search?key=%E7%83%A7%E7%81%AB&from=0&size=10）

　　


　　得到结果如图：

　　


　　成功调用。不过书上说，这种方法仅限于get方法。

　　OK，笔记完成，记录下来以防以后 用到可以参考参考。