中间件执行顺序（管道）

using System.Threading.Tasks;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Hosting;

namespace ConsoleApp2
{
    public static class Sample02
    {

        public static void Start()
        {

            var host = Host.CreateDefaultBuilder()
                .ConfigureWebHostDefaults(builder => builder
                    .Configure(app => app
                        .Use(Middleware1)                           //使用中间件
                        .Use(Middleware2)
                    )
                ).Build();
            host.Run();
        }

        private static RequestDelegate Middleware1(RequestDelegate next)
        {
            async Task App(HttpContext context)
            {
                await context.Response.WriteAsync("Middleware 1 Begin.");     //Step 1
                await next(context);                                         //跳转到下一个中间件
                await context.Response.WriteAsync("Middleware 1 End.");       //Step3
            }

            return App;
        }


        private static RequestDelegate Middleware2(RequestDelegate next)
        {
            async Task App(HttpContext context)
            {
                await context.Response.WriteAsync("Middleware 2 Begin.");        //没有就返回 //Step2
            }

            return App;
        }
    }
}