mvc的filter

如果想要記錄ajax的請求和輸出信息、內部發生異常記錄日志、需要登錄認證、需要權限判斷；那mvc的各種filter可以幫助你實現你想要的。Mvc框架支持5種不同類型的過濾器；我會按照執行順序進行簡單的demo,再簡單的代碼分享，萬一對一個人有益，也是值的。

1.通過實現IAuthenticationFilter來進行登錄認證，如果認證通過繼續后續的權限授權等操作；如果認證沒有通過跳轉登錄頁面；代碼如下：

public class MvcAuthenticationFilter : FilterAttribute, IAuthenticationFilter
    {
        /// <summary>
        /// 是否需要認證 
        /// </summary>
        public bool IsNeedAuthentication { get; set; }

        /// <summary>
        /// 對請求進行身份驗證
        /// </summary>
        /// <param name="filterContext"></param>
        public void OnAuthentication(AuthenticationContext filterContext)
        {
            bool flag = filterContext.ActionDescriptor.IsDefined(typeof(AllowAnonymousAttribute), true) || filterContext.ActionDescriptor.ControllerDescriptor.IsDefined(typeof(AllowAnonymousAttribute), true);
            if (flag)
            {
                return;
            }
            if (IsNeedAuthentication)
            {
                IPrincipal user;
                if (this.IsAuthenticated(filterContext, out user))
                {
                    filterContext.Principal = user;
                }
                else
                {
                    this.UnauthenticatedRequest(filterContext);
                }
            }
        }

        protected bool IsAuthenticated(AuthenticationContext filterContext, out IPrincipal user)
        {
            user = filterContext.HttpContext.User;
            var cc = filterContext.Controller.ControllerContext.Controller as BaseController;
            if (cc != null && cc.CurrentAdminInfo != null)
            {
                IIdentity identity = user.Identity;
                user = new GenericPrincipal(identity, new[] { "root", "noroot" }); //這里根據實際情況獲取用戶的角色
                return true;
            }
            return false;
        }

        protected void UnauthenticatedRequest(AuthenticationContext filterContext)
        {
            string returnUrl = filterContext.HttpContext.Request.Url.AbsolutePath;
            string redirectUrl = string.Format("?ReturnUrl={0}", returnUrl);
            string loginUrl = FormsAuthentication.LoginUrl + redirectUrl;
            filterContext.HttpContext.Response.Redirect(loginUrl, true);
        }
        public void OnAuthenticationChallenge(AuthenticationChallengeContext filterContext) { }
    }

2.每個管理后台都少不了權限判斷的需求；你可以使用[Authorize(Roles = "r1,r2")] 默認實現進行硬編碼，對於用戶的權限和角色經常變動的話，或者你需要靈活的處理就需要自定義Authorize，咱們先看下Authorize源代碼實現你就會明白

他的實現原理，先判斷是否有匿名訪問標簽，然后利用AuthorizeCore 授權檢查，如果未授權利用HandleUnauthorizedRequest 放回401，跳轉到登錄頁面；很明顯授權不通過跳轉登錄頁面不是太合適；另一種實現方式 自定義Authorize 代碼如下：

        public new string[] Roles { get; set; }
        protected override bool AuthorizeCore(HttpContextBase httpContext)
        {
            //由原來指定的roles 替換成動態讀取的。
            //跟登錄用戶的roles進行比較。
            if (httpContext == null)
            {
                throw new ArgumentNullException("httpContext");
            }
            if (!httpContext.User.Identity.IsAuthenticated)
            {
                return false;
            }
            if (Roles == null)
            {
                return true;
            }
            if (Roles.Length == 0)
            {
                return true;
            }
            if (Roles.Any(new Func<string, bool>(httpContext.User.IsInRole)))
            {
                return true;
            }
            httpContext.Response.StatusCode = 403;
            return false;
        }

        protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
        {
            filterContext.Result = new HttpUnauthorizedResult();
        }

        public override void OnAuthorization(AuthorizationContext filterContext)
        {

            bool flag = filterContext.ActionDescriptor.IsDefined(typeof(AllowAnonymousAttribute), true) || filterContext.ActionDescriptor.ControllerDescriptor.IsDefined(typeof(AllowAnonymousAttribute), true);
            if (flag)
            {
                return;
            }
            string controllerName = filterContext.ActionDescriptor.ControllerDescriptor.ControllerName;
            string actionName = filterContext.ActionDescriptor.ActionName;
            string roles = string.Join(",", GetRoles(actionName, controllerName));
            if (!string.IsNullOrWhiteSpace(roles))
            {
                this.Roles = roles.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);
            }

            base.OnAuthorization(filterContext);
            if (filterContext.HttpContext.Response.StatusCode == 403)
            {
                //跳轉未授權頁面
                filterContext.Result = new RedirectResult("/Other/Noright");
            }
        }

3.動作過濾器記錄一些ajax的輸入輸出數據，方便排查問題；代碼有注釋也比較簡單直接貼代碼了

  public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            if (filterContext.HttpContext.Request.IsAjaxRequest())
            {
                var httpContext = filterContext.HttpContext;
                //輸入參數
                var req = new JavaScriptSerializer().Serialize(HttpContext.Current.Request.Form.AllKeys.ToDictionary(k => k, k => HttpContext.Current.Request.Form[k]));
                var code = httpContext.Request.GetHashCode();
                var controllerName = filterContext.RouteData.Values["controller"] as string;
                var actionName = filterContext.RouteData.Values["action"] as string;
                var postUrl = controllerName + "/" + actionName;
                LogHelper.WriteDebug(
                    string.Format("RequestUrl:{0};HashCode:{1}</br>RequestParam{2}",
                   postUrl, code,
                    req));
            }
        }

   
        public override void OnActionExecuted(ActionExecutedContext filterContext)
        {
            if (filterContext.HttpContext.Request.IsAjaxRequest())
            {
                //輸出參數
                var jsonR = filterContext.Result as JsonResult;
                var res = new JavaScriptSerializer().Serialize(jsonR);
                LogHelper.WriteDebug(string.Format("OnActionExecuted---返回值:{0}", res));
            }

        }

4.最后是發生異常的處理，mvc默認實現HandleErrorAttribute，但是也不夠靈活，查看源代碼

 我們定義之后的代碼

    public override void OnException(ExceptionContext filterContext)
        {
            string errCode = "";
            string errMsg = "";
            //自定義錯誤
            if (filterContext.Exception is ClException)
            {
            }
            else
            {
                errMsg = "未知錯誤";
                LogHelper.WriteError(filterContext.Exception.Message);
            }
            //如果是ajax請求
            if (filterContext.HttpContext.Request.IsAjaxRequest())
            {
                var result = new ExceptionResponse
                {
                    ErrMsg = errMsg,
                };
                filterContext.Result = new JsonResult()
                {
                    Data = result
                };
            }//500服務器內部錯誤
            else
            {
                filterContext.Result = new ViewResult() { ViewName = "/Views/Other/Seerro.cshtml" };
            }

            filterContext.ExceptionHandled = true;//阻止golbal里的錯誤執行
            filterContext.HttpContext.Response.Clear();
            filterContext.HttpContext.Response.StatusCode = 500;
            filterContext.HttpContext.Response.TrySkipIisCustomErrors = true;//禁用 IIS 自定義錯誤
        }

 看下彈出的錯誤效果