asp.net core 系列之中間件進階篇-編寫自定義中間件(middleware)

時間 2019-11-11

標籤 asp.net asp core 系列中間件進階編寫自定義 middleware 欄目 ASP 简体版

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中間件是被用到管道(pipeline)上來處理請求(request)和響應的(response)。app

asp.net core 自己提供了一些內置的中間件，可是有一些場景，你可能會須要寫一些自定義的中間件。asp.net

1. 建立一個使用匿名委託的中間件組件的形式async

public class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        app.Use((context, next) =>
        {
            var cultureQuery = context.Request.Query["culture"];
            if (!string.IsNullOrWhiteSpace(cultureQuery))
            {
                var culture = new CultureInfo(cultureQuery);

                CultureInfo.CurrentCulture = culture;
                CultureInfo.CurrentUICulture = culture;
            }

            // Call the next delegate/middleware in the pipeline
            return next();
        });

        app.Run(async (context) =>
        {
            await context.Response.WriteAsync(
                $"Hello {CultureInfo.CurrentCulture.DisplayName}");
        });

    }
}

注：app.use中return next()會傳遞到下一個中間件繼續執行；而僅僅只使用app.use 的用法和app.run相同，即不會再傳遞到下一個中間件，在此做爲請求處理的結束ui

2.把中間件的委託封裝到類裏面，即把中間件寫成一個類的形式this

using Microsoft.AspNetCore.Http;
using System.Globalization;
using System.Threading.Tasks;

namespace Culture
{
    public class RequestCultureMiddleware
    {
        private readonly RequestDelegate _next;

        public RequestCultureMiddleware(RequestDelegate next)
        {
            _next = next;
        }

        public async Task InvokeAsync(HttpContext context)
        {
            var cultureQuery = context.Request.Query["culture"];
            if (!string.IsNullOrWhiteSpace(cultureQuery))
            {
                var culture = new CultureInfo(cultureQuery);

                CultureInfo.CurrentCulture = culture;
                CultureInfo.CurrentUICulture = culture;

            }

            // Call the next delegate/middleware in the pipeline
            await _next(context);
        }
    }
}

而後，再使用一箇中間件擴展方法，經過IApplicationBuilder使用中間件spa

using Microsoft.AspNetCore.Builder;

namespace Culture
{
    public static class RequestCultureMiddlewareExtensions
    {
        public static IApplicationBuilder UseRequestCulture(
            this IApplicationBuilder builder)
        {
            return builder.UseMiddleware<RequestCultureMiddleware>();
        }
    }
}

最後，在 Startup.Configure 中調用中間件.net

public class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        app.UseRequestCulture();  //調用中間件

        app.Run(async (context) =>
        {
            await context.Response.WriteAsync(
                $"Hello {CultureInfo.CurrentCulture.DisplayName}");
        });

    }
}

另外，這裏還有一點，這個地方不是很懂，說下本身的理解，歡迎大佬指正code

當中間件中注入的還有其餘service(官方叫 a scoped service )時，須要使用的是Invoke方法，而不是InvokeAsync方法中間件

public class CustomMiddleware
{
    private readonly RequestDelegate _next;

    public CustomMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    // IMyScopedService is injected into Invoke
    public async Task Invoke(HttpContext httpContext, IMyScopedService svc)
    {
        svc.MyProperty = 1000;
        await _next(httpContext);
    }
}