.Net Core MVC中过滤器简介

在.Net Framework MVC 中有四种过滤器，授权过滤器（Authorize）、Action 过滤器、结果过滤器（Result）、异常过滤器（Exception）四种过滤器。在.Net Core MVC中，有五种过滤器，授权过滤器、Action过滤器、异常过滤器、结果过滤器、资源过滤器，新增了资源过滤器。

.Net Core MVC和.Net Framework MVC在基本使用上差别不大，主要的还是框架的差别。其中路由是个很重要的东西，参考文章：https://www.cnblogs.com/durow/p/5992926.html

Action过滤器、结果过滤器、Exception，三个特性，没有什么变化。在ExceptionFilter多了个Order参数，就是用来排序的。

 

 

结果过滤器，包装了单个Action Result的执行，当且晋档Action方法成功执行完毕后才运行。它们是理想的围绕视图执行或格式处理的逻辑（所在之处）。继承Attribute，IResultFilter

 /// <summary>
 /// Result的Filter
 /// </summary>
 public class CustomResultFilterAttribute : Attribute, IResultFilter
 {
     //private Logger logger = Logger.CreateLogger(typeof(CustomResultFilterAttribute));
     public void OnResultExecuted(ResultExecutedContext context)
     {
         Console.WriteLine("OnResultExecuted Executed!");
         //logger.Info("OnResultExecuted Executed!");
     }

     public void OnResultExecuting(ResultExecutingContext context)
     {
         Console.WriteLine("OnResultExecuting Executing!");
         //logger.Info("OnResultExecuting Executing!");
     }
 }

异常过滤器，为MVC隐藏程序为处理异常应用全局策略。继承ExceptionFilterAttribute

 /// <summary>
 /// 异常处理的Filter
 /// </summary>
 public class CustomExceptionFilterAttribute : ExceptionFilterAttribute
 {
     private readonly IHostingEnvironment _hostingEnvironment;
     private readonly IModelMetadataProvider _modelMetadataProvider;
     //private Logger logger = Logger.CreateLogger(typeof(CustomExceptionFilterAttribute));

     /// <summary>
     /// IOC来的
     /// </summary>
     /// <param name="hostingEnvironment"></param>
     /// <param name="modelMetadataProvider"></param>
     public CustomExceptionFilterAttribute(
         IHostingEnvironment hostingEnvironment,
         IModelMetadataProvider modelMetadataProvider)
     {
         _hostingEnvironment = hostingEnvironment;
         _modelMetadataProvider = modelMetadataProvider;
     }

     /// <summary>
     /// 没有处理的异常，就会进来
     /// </summary>
     /// <param name="filterContext"></param>
     public override void OnException(ExceptionContext filterContext)
     {
         if (!filterContext.ExceptionHandled)//异常有没有被处理过
         {
             string controllerName = (string)filterContext.RouteData.Values["controller"];
             string actionName = (string)filterContext.RouteData.Values["action"];
             string msgTemplate = "在执行 controller[{0}] 的 action[{1}] 时产生异常";
             //logger.Error(string.Format(msgTemplate, controllerName, actionName), filterContext.Exception);
             if (this.IsAjaxRequest(filterContext.HttpContext.Request))//检查请求头
             {
                 filterContext.Result = new JsonResult(
                      new
                      {
                          Result = false,
                          PromptMsg = "系统出现异常，请联系管理员",
                          DebugMessage = filterContext.Exception.Message
                      }//这个就是返回的结果
                 );
             }
             else
             {
                 var result = new ViewResult { ViewName = "~/Views/Shared/Error.cshtml" };
                 result.ViewData = new ViewDataDictionary(_modelMetadataProvider, filterContext.ModelState);
                 result.ViewData.Add("Exception", filterContext.Exception);
                 filterContext.Result = result;
             }
             filterContext.ExceptionHandled = true;
         }
     }


     private bool IsAjaxRequest(HttpRequest request)
     {
         string header = request.Headers["X-Requested-With"];
         return "XMLHttpRequest".Equals(header);
     }
 }

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