今天來看一下asp.net core的執行管道。先看下官方說明：

 從上圖可以拋光，asp.net core的執行順序是，當收到一個請求後，request請求會先經過已註冊的中介軟體，然後會進入到mvc的攔截器管道：

進入mvc管道後，根據以上順序執行過濾校正。

OK，根據以上說明下面我們新建一個MVC的演示，將執行方式切換為控臺執行：

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    services.AddControllersWithViews(config=> 
    {
        Console.WriteLine("execute C");
        //config.Filters.Add(new AsyncAuthorizationFilter());
        config.Filters.Add(new AuthorizationFilter());
        config.Filters.Add(new ResourceFilter());
        //config.Filters.Add(new AsyncResourceFilter());
        config.Filters.Add(new ActionFilter());
        //config.Filters.Add(new AsyncActionFilter());
        config.Filters.Add(new ResultFilter());
        //config.Filters.Add(new AsyncResultFilter());
        config.Filters.Add(new ExceptionFilter());
        //config.Filters.Add(new AsyncExceptionFilter());
        Console.WriteLine("execute D");
    });
    services.AddSession(config=> {
        Console.WriteLine("execute E");
    });
}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
    }
    app.UseStaticFiles();
    app.UseRouting();
    app.UseAuthorization();
    app.Use(async (context, next) =>
    {
        Console.WriteLine("execute F");
        await context.Response.WriteAsync("hello world");
        Console.WriteLine("execute G");
    });
    //app.UseSession();
    app.UseEndpoints(endpoints =>
    {
        Console.WriteLine("execute A");
        endpoints.MapControllerRoute(
            name: "default",
            pattern: "{controller=Home}/{action=Index}/{id?}");
        Console.WriteLine("execute B");
    });
}

執行結果：

不多做解釋，從從這裡我們可以拋光符合官方說明文件。

看完中介軟體執行順序，下面我們來了解下mvc攔截器的使用與執行順序。

根據mvc filter管道執行順序，我們分別來看下用法：

1）AuthorizationFilter：該攔截器是優先順序最高的，當請求進入mvc後，首先會被AuthorizationFilter驗證是否有許可權訪問，無許可權則跳出。

同步用法：

public class AuthorizationFilter: IAuthorizationFilter
{
    public void OnAuthorization(AuthorizationFilterContext context)
    {
        context.HttpContext.Response.WriteAsync("authorization filter \r");
    }
}

非同步用法：

public class AsyncAuthorizationFilter: IAsyncAuthorizationFilter
{
    public async Task OnAuthorizationAsync(AuthorizationFilterContext context)
    {
        await context.HttpContext.Response.WriteAsync($"async authorization filter in \r");
    }
}

2）ResourceFilter：該攔截器是作為第二道攔截器，

OnResourceExecuting在模型繫結之前執行程式碼。OnResourceExecuted在管道的其餘階段完成之後執行程式碼。

同步用法：

public class ResourceFilter: IResourceFilter
{
    public void OnResourceExecuting(ResourceExecutingContext context)
    {
        context.HttpContext.Response.WriteAsync($"resource executing\r");
    }
    public void OnResourceExecuted(ResourceExecutedContext context)
    {
        context.HttpContext.Response.WriteAsync($"resource executed \r");
    }
}

非同步用法：

public class AsyncResourceFilter: IAsyncResourceFilter
{
    public async Task OnResourceExecutionAsync(ResourceExecutingContext context, ResourceExecutionDelegate next)
    {
        await context.HttpContext.Response.WriteAsync($" async resource filter in. \r\n");
        await next();
        await context.HttpContext.Response.WriteAsync($"async resource filter out. \r\n");
    }
}

3）ActionFilter：在呼叫操作方法之前和之後立即執行程式碼；可以更改傳遞到操作中的引數；可以更改從操作返回的結果。

同步用法：

public class ActionFilter: IActionFilter
{
    public void OnActionExecuting(ActionExecutingContext context)
    {
        context.HttpContext.Response.WriteAsync($"action executing \r");
    }

    public void OnActionExecuted(ActionExecutedContext context)
    {
        context.HttpContext.Response.WriteAsync($"action executed . \r");
    }
}

非同步用法：

public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
{
    await context.HttpContext.Response.WriteAsync($"async action execution in. \r\n");
    await next();
    await context.HttpContext.Response.WriteAsync($"async action execution out. \r\n");
}

4）OnException：在向響應正文寫入任何內容之前，對宣告處理的異常應用變數策略。

同步用法：

public class ExceptionFilter: IExceptionFilter
{
    public void OnException(ExceptionContext context)
    {
        context.HttpContext.Response.WriteAsync($"exception \r");
    }
}

非同步用法：

public class AsyncExceptionFilter: IAsyncExceptionFilter
{
    public Task OnExceptionAsync(ExceptionContext context)
    {
        context.HttpContext.Response.WriteAsync($"exception async \r");
        return Task.CompletedTask;
    }
}

5）ResultFilter：在執行操作結果之前和之後立即執行程式碼；僅當操作方法成功執行時，其才會執行。 可以設定格式化返回結果： 

同步操作：

public class ResultFilter: IResultFilter
{
    public void OnResultExecuting(ResultExecutingContext context)
    {
        context.HttpContext.Response.WriteAsync($"result executing\r");
    }
    public void OnResultExecuted(ResultExecutedContext context)
    {
        context.HttpContext.Response.WriteAsync($"result executed \r");
    }
}

非同步用法：

public class AsyncResultFilter: IAsyncResultFilter
{
    public async Task OnResultExecutionAsync(ResultExecutingContext context, ResultExecutionDelegate next)
    {
        await context.HttpContext.Response.WriteAsync($"result execution async in \r");
        await next();
        await context.HttpContext.Response.WriteAsync($"result execution async out. \r");
    }
}

註冊方式我們就是用分割槽註冊，已經在上面說明，不再多做表述，下面我們看下執行情況（頁面輸出）：

 定義一個異常看下結果：

public IActionResult Privacy()
{
    throw new Exception("error");
}

ok，目標達成，不多說了，下次再看攔截器具體實現。

參考文件：ASP.NET Core 中的篩選器

原創，轉載註明出處。

&n