27-Middleware管道介绍

 public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.Map("/task",taskApp=>{ //路由匹配
                taskApp.Run(async (context)=>{
                    await context.Response.WriteAsync("i am task");
                });
            });
            app.Use(async (context,next) => {
                 await  context.Response.WriteAsync("start1.....");
                 await  next.Invoke();
            });

            app.Use( next =>
            {
                    return (context)=>{
                        context.Response.WriteAsync("middle....");
                        return next(context); //如果不调用next方法，下面的end不会显示
                    };
            });

            app.Run(async (context) =>
            {
               await context.Response.WriteAsync("end........");
            });
        }