問題場景：

對於處理介面返回值統一加密，過濾，特定值統一處理，統一返回等多種需求，net的攔截器前置攔截比較常用，例如：登入校驗，引數格式校驗等等。接下來介紹filter

filter過濾器實現

filter的ActionFilterAttribute可以做一定的處理，通過對OnActionExecuted的執行控制，來實現很多場景。ActionFilterAttribute類是C# ASP.net MVC中的過濾類，跟JAVA的Filter效果類似，但是Filter是介面。ActionFilterAttribute類是被abstract 修飾符修飾，表示該類只能是基類，也就是隻能被繼承。ActionFilterAttribute類中只有一個無引數的建構函式和四個被protected 修飾符修飾，表示該方法只限於本類和子類訪問，例項不能訪問。

 /// <summary>
    /// Service返回資料過濾器，為返回的資料增加返回碼和訊息
    /// </summary>
    public class ReturnDataFilterAttribute : ActionFilterAttribute
    {
        private static JsonMediaTypeFormatter _formatter;

        static ReturnDataFilterAttribute()
        {
            _formatter = new JsonMediaTypeFormatter();
            
 
//設定序列化器為json序列化器
            //            _formatter.UseDataContractJsonSerializer = true;
            //設定時間格式為Local
            _formatter.SerializerSettings.DateTimeZoneHandling = Newtonsoft.Json.DateTimeZoneHandling.Local;
            _formatter.SerializerSettings.DateFormatString = "yyyy-MM-ddTHH:mm:ss.fffzz:00
 
";
            //設定縮排
            _formatter.SerializerSettings.Formatting = Newtonsoft.Json.Formatting.Indented;
            //設定json格式為駝峰式
            _formatter.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
        }

        public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
        {
            if (actionExecutedContext.Response != null)
            {
                var oldResponse = actionExecutedContext.Response;
                //response狀態為請求成功
                var result = new System.Net.Http.HttpResponseMessage(System.Net.HttpStatusCode.OK);
                if (ApiMatch(ConfigHelper.GetAppSetting("IgnoreReturnDataFilter"),
                        actionExecutedContext.Request.RequestUri.AbsolutePath))
                {
                    result.Content = oldResponse.Content;
                }
                else
                {
                object content = null;
                var objectContent = oldResponse.Content as ObjectContent;
                if (objectContent != null)
                {
                    content = objectContent.Value;
                }
                //把action返回的值放到ReturnData的Result中
                result.Content =
                    new ObjectContent<ReturnData>(
                        new ReturnData {Msg = "成功", Ret = CustomException.NoneError, Result = content},
                        _formatter);
                }
                actionExecutedContext.Response = result;
            }
        }

        /// <summary>
        /// API資料中的API是否匹配請求URIi
        /// </summary>
        /// <param name="apiArray">API資料</param>
        /// <param name="uri">請求URI</param>
        /// <returns>是否匹配</returns>
        private static bool ApiMatch(string apiArray, string uri)
        {
            var result = false;
            if (!string.IsNullOrWhiteSpace(apiArray))
            {
                var apiList = apiArray.ToLower().Split(',');
                string uriLower = uri.ToLower();
                foreach (var api in apiList)
                {
                    if (api == uriLower || api + "/" == uriLower)
                    {
                        result = true;
                        break;
                    }
                }
            }
            return result;
        }
    }

     //返回資料過濾器
    config.Filters.Add(new ReturnDataFilterAttribute());