.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);

     }

 }

定义完ExceptionFilter，该怎么注册到全局呢？在Stratup.cs中ConfigureServer中，进行注册

services.AddMvc(o =>

{

    o.Filters.Add(typeof(CustomExceptionFilterAttribute));// 这里就是全局注册Filter

}).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

Action 过滤器，包装了对单个Action方法的调用，可以将参数传递给Action并从中获得Action Result。继承IActionFilter

 /// <summary>

 /// Action的Filter`

 /// </summary>

 public class CustomActionFilterAttribute : Attribute, IActionFilter

 {

     private ILogger<CustomActionFilterAttribute> _logger = null;

     public CustomActionFilterAttribute(ILogger<CustomActionFilterAttribute> logger)

     {

         this._logger = logger;

     }

     public void OnActionExecuted(ActionExecutedContext context)

     {

         //context.HttpContext.Response.WriteAsync("ActionFilter Executed!");

         Console.WriteLine("ActionFilter Executed!");

         //this._logger.LogDebug("ActionFilter Executed!");

     }

     public void OnActionExecuting(ActionExecutingContext context)

     {

         //context.HttpContext.Response.WriteAsync("ActionFilter Executing!");

         Console.WriteLine("ActionFilter Executing!");

         //this._logger.LogDebug("ActionFilter Executing!");

     }

 }

在Startup.cs中ConfigureServices进行注册

 //允许使用ServiceFilter 标记特性

 services.AddScoped<CustomActionFilterAttribute>();

标记到Controller的ActionFilter

/// <summary>

/// 标记到Controller

/// </summary>

public class CustomControllerActionFilterAttribute : Attribute, IActionFilter

{

    private ILogger<CustomControllerActionFilterAttribute> _logger = null;

    public CustomControllerActionFilterAttribute(ILogger<CustomControllerActionFilterAttribute> logger)

    {

        this._logger = logger;

    }

    public void OnActionExecuted(ActionExecutedContext context)

    {

        //context.HttpContext.Response.WriteAsync("ActionFilter Executed!");

        Console.WriteLine("ActionFilter Executed!");

        //this._logger.LogDebug("ActionFilter Executed!");

    }

    public void OnActionExecuting(ActionExecutingContext context)

    {

        //context.HttpContext.Response.WriteAsync("ActionFilter Executing!");

        Console.WriteLine("ActionFilter Executing!");

        //this._logger.LogDebug("ActionFilter Executing!");

    }

}

 [TypeFilter(typeof(CustomControllerActionFilterAttribute),Order =-)]

 public class ThirdController : Controller

 {

}

注册到全局的ActionFilter

public class CustomGlobalActionFilterAttribute : Attribute, IActionFilter

{

    private ILogger<CustomGlobalActionFilterAttribute> _logger = null;

    public CustomGlobalActionFilterAttribute(ILogger<CustomGlobalActionFilterAttribute> logger)

    {

        this._logger = logger;

    }

    public void OnActionExecuted(ActionExecutedContext context)

    {

        //context.HttpContext.Response.WriteAsync("ActionFilter Executed!");

        Console.WriteLine("ActionFilter Executed!");

        //this._logger.LogDebug("ActionFilter Executed!");

    }

    public void OnActionExecuting(ActionExecutingContext context)

    {

        //context.HttpContext.Response.WriteAsync("ActionFilter Executing!");

        Console.WriteLine("ActionFilter Executing!");

        //this._logger.LogDebug("ActionFilter Executing!");

    }

}

还是要在Startup中进行全局的注册

services.AddMvc(o =>

{

    o.Filters.Add(typeof(CustomGlobalActionFilterAttribute));// 这里就是全局注册Filter

}).SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

分别对全局、控制器、Action注册了ActionFilter默认执行顺序：

　　全局OnActionExecuting===》控制器的OnActionExecuting====》Action的OnActionExecuting====》执行Action ====》Action的OnActionExecuted====》控制器的OnActionExecuted====》全局的OnActionExecuted。类似于一个俄罗斯套娃，也可以说是一个洋葱模型。

资源过滤器，是授权之后第一个用来处理请求的过滤器，也是最后一个接触到请求的过滤器（因为之后就会离开过滤器管道）。在性能方面，资源过滤器在实现缓存或短路过滤器管道尤其有用。继承IResourceFilter

 /// <summary>

 /// 自定义的资源Filter

 /// </summary>

 public class CustomResourceFilterAttribute : Attribute, IResourceFilter

 {

     private static readonly Dictionary<string, object> _Cache = new Dictionary<string, object>();

     private string _cacheKey;

     /// <summary>

     /// 控制器实例化之前

     /// </summary>

     /// <param name="context"></param>

     public void OnResourceExecuting(ResourceExecutingContext context)

     {

         _cacheKey = context.HttpContext.Request.Path.ToString();

         if (_Cache.ContainsKey(_cacheKey))

         {

             var cachedValue = _Cache[_cacheKey] as ViewResult;

             if (cachedValue != null)

             {

                 context.Result = cachedValue;

             }

         }

     }

     /// <summary>

     /// 把请求都处理完的

     /// </summary>

     /// <param name="context"></param>

     public void OnResourceExecuted(ResourceExecutedContext context)

     {

         if (!String.IsNullOrEmpty(_cacheKey) &&

             !_Cache.ContainsKey(_cacheKey))

         {

             var result = context.Result as ViewResult;

             if (result != null)

             {

                 _Cache.Add(_cacheKey, result);

             }

         }

     }

 }

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.Net Core MVC中过滤器简介

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