ASP.NET Core 2 學習筆記（十四）Filters

時間  2019-12-13
標籤 asp.net asp core 學習 筆記 十四 filters 欄目 ASP 简体版
原文   原文鏈接

Filter是延續ASP.NET MVC的產物，一樣保留了五種的Filter，分別是Authorization Filter、Resource Filter、Action Filter、Exception Filter及Result Filter。
經過不一樣的Filter能夠有效處理封包進出的加工，本篇將介紹ASP.NET Core的五種Filter運做方式。git

Filter 介紹

Filter的做用是在Action 執行前或執行後作一些加工處理。
某種程度來看，會跟Middleware很像，但執行的順序略有不一樣，用對Filter不只能夠減小代碼，還能夠提升執行效率。github

ASP.NET Core 有如下五種Filter 可使用：bash

  • Authorization Filter
    Authorization是五種Filter中優先級最高的，一般用於驗證Request合不合法，不合法後面就直接跳過。
  • Resource Filter
    Resource是第二優先，會在Authorization以後，Model Binding以前執行。一般會是須要對Model加工處理才用。
  • Action Filter
    最常使用的Filter，封包進出都會通過它，使用上沒什麼須要特別注意的。跟Resource Filter很相似，但並不會通過Model Binding。
  • Exception Filter
    異常處理的Filter。
  • Result Filter
    當Action完成後，最終會通過的Filter。

Filter 運做方式

ASP.NET Core的每一個Request都會先通過已註冊的Middleware接着纔會執行Filter，除了會依照上述的順序外，同類型的Filter預設都會以先進後出的方式處裏封包。
Response在某些Filter並不會作處理，會直接被pass。Request及Response的運做流程以下圖：mvc

  • 黃色箭頭是正常狀況流程
  • 灰色箭頭是異常處理流程

創建Filter

ASP.NET Core的Filter基本上跟ASP.NET MVC的差很少。
上述的五種Filter範例分別以下：async

Authorization Filter

AuthorizationFilter.csspa

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Filters;

namespace MyWebsite.Filters
{
    public class AuthorizationFilter : IAuthorizationFilter
    {
        public void OnAuthorization(AuthorizationFilterContext context)
        {
            context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
        }
    }
}

非同步的方式：code

// ...
public class AuthorizationFilter : IAsyncAuthorizationFilter
{
    public async Task OnAuthorizationAsync(AuthorizationFilterContext context)
    {
        await context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
    }
}

Resource Filter

ResourceFilter.csblog

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Filters;

namespace MyWebsite.Filters
{
    public class ResourceFilter : IResourceFilter
    {
        public void OnResourceExecuting(ResourceExecutingContext context)
        {
            context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
        }

        public void OnResourceExecuted(ResourceExecutedContext context)
        {
            context.HttpContext.Response.WriteAsync($"{GetType().Name} out. \r\n");
        }
    }
}

非同步的方式：繼承

// ...
public class ResourceFilter : IAsyncResourceFilter
{
    public async Task OnResourceExecutionAsync(ResourceExecutingContext context, ResourceExecutionDelegate next)
    {
        await context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");

        await next();

        await context.HttpContext.Response.WriteAsync($"{GetType().Name} out. \r\n");
    }
}

Action Filter

ActionFilter.csget

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Filters;

namespace MyWebsite.Filters
{
    public class ActionFilter : IActionFilter
    {
        public void OnActionExecuting(ActionExecutingContext context)
        {
            context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
        }

        public void OnActionExecuted(ActionExecutedContext context)
        {
            context.HttpContext.Response.WriteAsync($"{GetType().Name} out. \r\n");
        }
    }
}

非同步的方式：

// ...
public class ActionFilter : IAsyncActionFilter
{
    public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
        await context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");

        await next();

        await context.HttpContext.Response.WriteAsync($"{GetType().Name} out. \r\n");
    }
}

Result Filter

ResultFilter.cs

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Filters;

namespace MyWebsite.Filters
{
    public class ResultFilter : IResultFilter
    {
        public void OnResultExecuting(ResultExecutingContext context)
        {
            context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
        }

        public void OnResultExecuted(ResultExecutedContext context)
        {
            context.HttpContext.Response.WriteAsync($"{GetType().Name} out. \r\n");
        }
    }
}

非同步的方式：

// ...
public class ResultFilter : IAsyncResultFilter
{
    public async Task OnResultExecutionAsync(ResultExecutingContext context, ResultExecutionDelegate next)
    {
        await context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");

        await next();

        await context.HttpContext.Response.WriteAsync($"{GetType().Name} out. \r\n");
    }
}

Exception Filter

ExceptionFilter.cs

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc.Filters;

namespace MyWebsite.Filters
{
    public class ExceptionFilter : IExceptionFilter
    {
        public void OnException(ExceptionContext context)
        {
            context.ExceptionHandled = true; // 代表異常已處理，客戶端可獲得正常返回
            context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
        }
    }
}

非同步的方式：

// ...
public class ExceptionFilter : IAsyncExceptionFilter
{
        public Task OnExceptionAsync(ExceptionContext context)
        {
            context.ExceptionHandled = true;// 代表異常已處理，客戶端可獲得正常返回
            context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
            return Task.CompletedTask;
        }
}

註冊Filter

Filter有兩種註冊方式，一種是全局註冊，另外一種是用[Attribute]局部註冊的方式，只套用在特定的Controller或Action。

全局註冊

在Startup.ConfigureServices的MVC服務中註冊Filter，這樣就能夠套用到全部的Request。以下：

// ...
public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc(config =>
        {
            config.Filters.Add(new ResultFilter());
            config.Filters.Add(new ExceptionFilter());
            config.Filters.Add(new ResourceFilter());
        });
    }
}

局部註冊

ASP.NET Core在局部註冊Filter的方式跟ASP.NET MVC有一點不同，要經過[TypeFilter(type)]。
在Controller或Action上面加上[TypeFilter(type)]就能夠局部註冊Filter。以下：

// ...
namespace MyWebsite.Controllers
{
    [TypeFilter(typeof(AuthorizationFilter))]
    public class HomeController : Controller
    {
        [TypeFilter(typeof(ActionFilter))]
        public void Index()
        {
            Response.WriteAsync("Hello World! \r\n");
        }
        
        [TypeFilter(typeof(ActionFilter))]
        public void Error()
        {
            throw new System.Exception("Error");
        }
    }
}

[TypeFilter(type)]用起來有點冗長，想要像過去ASP.NET MVC用[Attribute]註冊Filter的話，只要將Filter繼承Attribute便可。以下：

public class AuthorizationFilter : Attribute, IAuthorizationFilter
{
    // ...
}
public class ActionFilter : Attribute, IActionFilter
{
    // ...
}

[Attribute] 註冊就能夠改爲以下方式：

// ...
namespace MyWebsite.Controllers
{
    [AuthorizationFilter]
    public class HomeController : Controller
    {
        [ActionFilter]
        public void Index()
        {
            Response.WriteAsync("Hello World! \r\n");
        }
        
        [ActionFilter]
        public void Error()
        {
            throw new System.Exception("Error");
        }
    }
}

執行結果

http://localhost:5000/Home/Index 輸出結果以下：

AuthorizationFilter in.
ResourceFilter in.
ActionFilter in.
Hello World!
ActionFilter out.
ResultFilter in.
ResultFilter out.
ResourceFilter out.

http://localhost:5000/Home/Error 輸出結果以下：

AuthorizationFilter in.
ResourceFilter in.
ActionFilter in.
ActionFilter out.
ExceptionFilter in.
ResourceFilter out.

執行順序

預設註冊同類型的Filter 是以先進後出的方式處裏封包，註冊層級也會影響執行順序。

但也能夠經過實現 IOrderedFilter 更改執行順序。例如：

public class ActionFilter : Attribute, IActionFilter, IOrderedFilter
{
    public string Name { get; set; }

    public int Order { get; set; } = 0;

    public void OnActionExecuting(ActionExecutingContext context)
    {
        context.HttpContext.Response.WriteAsync($"{GetType().Name}({Name}) in. \r\n");
    }
    public void OnActionExecuted(ActionExecutedContext context)
    {
        context.HttpContext.Response.WriteAsync($"{GetType().Name}({Name}) out. \r\n");
    }
}

在註冊Filter 時帶上Order，數值越小優先權越高。

// ...
public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc(config =>
        {
            config.Filters.Add(new ActionFilter() { Name = "Global", Order = 3 });
        });
    }
}

// ...
namespace MyWebsite.Controllers
{
    [ActionFilter(Name = "Controller", Order = 2)]
    public class HomeController : Controller
    {
        [ActionFilter(Name = "Action", Order = 1)]
        public void Index()
        {
            Response.WriteAsync("Hello World! \r\n");
        }
    }
}

變動執行順序後的輸出內容：

ActionFilter(Action) in. 
ActionFilter(Controller) in. 
ActionFilter(Global) in. 
Hello World! 
ActionFilter(Global) out. 
ActionFilter(Controller) out. 
ActionFilter(Action) out.

參考

ASP.NET Core Filters

 

老司機發車啦：https://github.com/SnailDev/SnailDev.NETCore2Learning  

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