大多数人用MVC做项目处理异常时，只监听了IExceptionFilter  接口，这种做饭是不标准的，在应用程序未进入控制器或调用第三方插件（如富文本编辑器上传图片等，并不是所有第三方插件错误都监听不到）出问题时IExceptionFilter  接口是捕获不到错误的.

所以在Global.asax中捕获异常时很必要的，只需在IExceptionFilter  接口中把处理过的异常标记为已解决，Global.asax中是捕获不到此异常的。

MVC异常处理：

 public class ExceptionFilter : FilterAttribute, IExceptionFilter
    {
        void IExceptionFilter.OnException(ExceptionContext filterContext)
        {
            var ex = filterContext.Exception;

            var msg = ex.Message + " \r\n";
            msg += "\r\r\r\r" + ex.InnerException + " \r\n";
            msg += ex.StackTrace + " \r\n";

            filterContext.HttpContext.Response.WriteFile("~/views/shared/error.html");
            filterContext.HttpContext.Response.End();

            filterContext.ExceptionHandled = true;//标记此异常为已解决

        }
    }

Global.asax 中异常处理：

 protected void Application_Error(object sender, EventArgs e)
        {
            Exception ex = HttpContext.Current.Server.GetLastError();
            if (ex.GetType() == typeof(HttpException)) return;//不捕获http异常
            string errorMessage = BuildErrorMessage(ex);
            string msg = "--------------------header---------------------------------- \r\n";
            msg += DateTime.Now.ToString("yyyy-MM-dd hh:mm:ss") + " \r\n";
            msg += BuildErrorMessage(ex) + " \r\n";
            msg += ex.StackTrace + " \r\n";
            msg += "----------------------footer-------------------------------\r\n";
            string directory = Server.MapPath(string.Format("\\log\\OtherError\\{0}\\", DateTime.Now.ToString("yyyyMM")));
            if (!System.IO.Directory.Exists(directory))
                System.IO.Directory.CreateDirectory(directory);
            System.IO.File.AppendAllText(directory + DateTime.Now.ToString("yyyyMMdd") + ".log", msg + Environment.NewLine, System.Text.Encoding.Default);
            Server.ClearError();//清楚解决的异常
        }
        private string BuildErrorMessage(Exception ex)
        {
            while (ex.InnerException != null)
            {
                ex = ex.InnerException;
            }
            return ex.Message;
        }