背景

对于处理接口返回值统一加密，过滤，特定值统一处理，统一返回等多种需求，net的拦截器前置拦截比较常用，例如：登录校验，参数格式校验等等。接下来介绍filter。

filter过滤器实现

filter的ActionFilterAttribute可以做一定的处理，通过对OnActionExecuted的执行控制，来实现很多场景。ActionFilterAttribute类是C# ASP.net MVC中的过滤类，跟JAVA的Filter效果类似，但是Filter是接口。ActionFilterAttribute类是被abstract 修饰符修饰，表示该类只能是基类，也就是只能被继承。ActionFilterAttribute类中只有一个无参数的构造函数和四个被protected 修饰符修饰，表示该方法只限于本类和子类访问，实例不能访问。

代码实现

/// <summary>/// Service返回数据过滤器，为返回的数据增加返回码和消息/// </summary>public class ReturnDataFilterAttribute : ActionFilterAttribute{private static JsonMediaTypeFormatter _formatter;static ReturnDataFilterAttribute(){_formatter = new JsonMediaTypeFormatter();//设置序列化器为json序列化器//            _formatter.UseDataContractJsonSerializer = true;//设置时间格式为Local_formatter.SerializerSettings.DateTimeZoneHandling = Newtonsoft.Json.DateTimeZoneHandling.Local;_formatter.SerializerSettings.DateFormatString = "yyyy-MM-ddTHH:mm:ss.fffzz:00";//设置缩进_formatter.SerializerSettings.Formatting = Newtonsoft.Json.Formatting.Indented;//设置json格式为驼峰式_formatter.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();}public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext){if (actionExecutedContext.Response != null){var oldResponse = actionExecutedContext.Response;//response状态为请求成功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数据中的API是否匹配请求URIi/// </summary>/// <param name="apiArray">API数据</param>/// <param name="uri">请求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;}}

//返回数据过滤器config.Filters.Add(new ReturnDataFilterAttribute());