ASP.NET Core Middleware管道介绍

        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            app.Use(next => {
                return async context => {
                    await context.Response.WriteAsync("A11111111</br>");
                    await next.Invoke(context); //下一中间件
                    await context.Response.WriteAsync("B11111111</br>");
                };
            });
            app.Use(next => {
                return async context => {
                    await context.Response.WriteAsync("A22222222</br>");
                    await next.Invoke(context); //下一中间件
                    await context.Response.WriteAsync("B22222222</br>");
                };
            });
            app.Use(next => {
                return async context => {
                    await context.Response.WriteAsync("A33333333</br>");
                    await context.Response.WriteAsync("B33333333</br>");
                };
            });

        }

运行的时候是先执行3->2->1 倒序

自己动手构建RequestDelegate管道

    class Program
    {
        static void Main(string[] args)
        {
            ApplicationBuilder app = new ApplicationBuilder();
            app.Use(next =>
            {
                return async context =>
                {
                    await context.WriteAsync("A11111111\r\n");
                    await next.Invoke(context); //下一中间件
                    await context.WriteAsync("B11111111\r\n");
                };
            });
            app.Use(next =>
            {
                return async context =>
                {
                    await context.WriteAsync("A22222222\r\n");
                    await next.Invoke(context); //下一中间件
                    await context.WriteAsync("B22222222\r\n");
                };
            });
            app.Use(next =>
            {
                return async context =>
                {
                    await context.WriteAsync("A33333333\r\n");
                    await context.WriteAsync("B33333333\r\n");
                };
            });
            var requestDelegate = app.Build();
            requestDelegate.Invoke(new HttpContext());
            Console.ReadLine();
        }

        public delegate Task RequestDelegate(HttpContext context);

        public class HttpContext
        {
            public async Task WriteAsync(string text)
            {
                Console.WriteLine(text);
                await Task.CompletedTask;
            }
        }

        public class ApplicationBuilder
        {
            public List<Func<RequestDelegate, RequestDelegate>> _list = new List<Func<RequestDelegate, RequestDelegate>>();
            RequestDelegate requestDelegate = new RequestDelegate(async context =>
            {
                Console.WriteLine("404\r\n");
                await Task.CompletedTask;
            });

            public RequestDelegate Build()
            {
                _list.Reverse();
                foreach (var func in _list)
                {
                    requestDelegate = func.Invoke(requestDelegate);
                }
                return requestDelegate;
            }

            public ApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware)
            {
                this._list.Add(middleware);
                return this;
            }
        }
    }