Filter是延續(xù)ASP.NET MVC的產(chǎn)物，同樣保留了五種的Filter，分別是Authorization Filter、Resource Filter、Action Filter、Exception Filter及Result Filter。
通過不同的Filter可以有效處理封包進出的加工，本篇將介紹ASP.NET Core的五種Filter運作方式。
Filter 介紹
Filter的作用是在Action 執(zhí)行前或執(zhí)行后做一些加工處理。
某種程度來看，會跟Middleware很像，但執(zhí)行的順序略有不同，用對Filter不僅可以減少代碼，還可以提高執(zhí)行效率。
ASP.NET Core 有以下五種Filter 可以使用：
-
Authorization Filter
Authorization是五種Filter中優(yōu)先級最高的，通常用于驗證Request合不合法，不合法后面就直接跳過。 -
Resource Filter
Resource是第二優(yōu)先，會在Authorization之后，Model Binding之前執(zhí)行。通常會是需要對Model加工處理才用。 -
Action Filter
最常使用的Filter，封包進出都會經(jīng)過它，使用上沒什么需要特別注意的。跟Resource Filter很類似，但并不會經(jīng)過Model Binding。 -
Exception Filter
異常處理的Filter。 -
Result Filter
當(dāng)Action完成后，最終會經(jīng)過的Filter。
Filter 運作方式
ASP.NET Core的每個Request都會先經(jīng)過已注冊的Middleware接著才會執(zhí)行Filter，除了會依照上述的順序外，同類型的Filter預(yù)設(shè)都會以先進后出的方式處里封包。
Response在某些Filter并不會做處理，會直接被pass。Request及Response的運作流程如下圖：
- 黃色箭頭是正常情況流程
- 灰色箭頭是異常處理流程
建立Filter
ASP.NET Core的Filter基本上跟ASP.NET MVC的差不多。
上述的五種Filter范例分別如下：
Authorization Filter
AuthorizationFilter.cs
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($"{GetType().Name} in. \r\n");
}
}
}
非同步的方式：
// ...
public class AuthorizationFilter : IAsyncAuthorizationFilter
{
public async Task OnAuthorizationAsync(AuthorizationFilterContext context)
{
await context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
}
}
Resource Filter
ResourceFilter.cs
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：
// ...
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.cs
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; // 表明異常已處理，客戶端可得到正常返回
context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
}
}
}
非同步的方式：
// ...
public class ExceptionFilter : IAsyncExceptionFilter
{
public Task OnExceptionAsync(ExceptionContext context)
{
context.ExceptionHandled = true;// 表明異常已處理，客戶端可得到正常返回
context.HttpContext.Response.WriteAsync($"{GetType().Name} in. \r\n");
return Task.CompletedTask;
}
}
注冊Filter
Filter有兩種注冊方式，一種是全局注冊，另一種是用[Attribute]局部注冊的方式，只套用在特定的Controller或Action。
全局注冊
在Startup.ConfigureServices的MVC服務(wù)中注冊Filter，這樣就可以套用到所有的Request。如下：
// ...
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());
});
}
}
局部注冊
ASP.NET Core在局部注冊Filter的方式跟ASP.NET MVC有一點不一樣，要通過[TypeFilter(type)]。
在Controller或Action上面加上[TypeFilter(type)]就可以局部注冊Filter。如下：
// ...
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]注冊Filter的話，只要將Filter繼承Attribute即可。如下：
public class AuthorizationFilter : Attribute, IAuthorizationFilter
{
// ...
}
public class ActionFilter : Attribute, IActionFilter
{
// ...
}
[Attribute] 注冊就可以改成如下方式：
// ...
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(zhí)行結(jié)果
http://localhost:5000/Home/Index 輸出結(jié)果如下：
AuthorizationFilter in.
ResourceFilter in.
ActionFilter in.
Hello World!
ActionFilter out.
ResultFilter in.
ResultFilter out.
ResourceFilter out.
http://localhost:5000/Home/Error 輸出結(jié)果如下：
AuthorizationFilter in.
ResourceFilter in.
ActionFilter in.
ActionFilter out.
ExceptionFilter in.
ResourceFilter out.
執(zhí)行順序
預(yù)設(shè)注冊同類型的Filter 是以先進后出的方式處里封包，注冊層級也會影響執(zhí)行順序。
但也可以通過實現(xiàn) IOrderedFilter 更改執(zhí)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");
}
}
在注冊Filter 時帶上Order，數(shù)值越小優(yōu)先權(quán)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");
}
}
}
變更執(zhí)行順序后的輸出內(nèi)容：
ActionFilter(Action) in.
ActionFilter(Controller) in.
ActionFilter(Global) in.
Hello World!
ActionFilter(Global) out.
ActionFilter(Controller) out.
ActionFilter(Action) out.
