详解C#如何自定义书写中间件

/// <summary>
    /// 中间件定义和业务逻辑
    /// </summary>
    public class MyMiddleware
    {
        private readonly RequestDelegate _next;
        /// <summary>
        /// 构造
        /// </summary>
        /// <param name="next"></param>
        public MyMiddleware(RequestDelegate next)
        {
            _next = next;
        }
        /// <summary>
        /// 方法名必须命名为 Invoke或者 InvokeAsync,才能有效执行下一个中间件
        /// </summary>
        /// <param name="httpContext"></param>
        /// <returns></returns>
        public async Task InvokeAsync(HttpContext httpContext)
        {
            /*
             * 在这里可以书写业务处理逻辑
             *中间件的处理流程就像一个俄罗斯套娃，微软约定中间件需要两个参数，一个是httpcontext上下文对象，一个是Task类型的委托。
             * 通过上下文对象，处理请求，通过委托传递上下文对象到下一个中间件（这也是套娃模式的由来）。
             */
            try
            {
                await _next(httpContext);
            }
            catch (Exception ex)
            {
                //内部出现异常
                httpContext.Response.StatusCode = 500;
            }
            finally
            {
                var statusCode = httpContext.Response.StatusCode;
                var msg = "";
                switch (statusCode)
                {
                    case 401:
                        msg = "未授权";
                        break;
                    case 403:
                        msg = "拒绝访问";
                        break;
                    case 404:
                        msg = "未找到服务";
                        break;
                    case 405:
                        msg = "405 Method Not Allowed";
                        break;
                    case 500:
                        msg = "服务器内部错误";
                        break;
                    case 502:
                        msg = "请求错误";
                        break;
                }
                if (!string.IsNullOrWhiteSpace(msg))
                {
                    await HandleExceptionAsync(httpContext, msg);
                }
            }
        }
        /// <summary>
        /// 处理Http响应异常
        /// </summary>
        /// <param name="httpContext"></param>
        /// <param name="msg"></param>
        /// <returns></returns>
        private async Task HandleExceptionAsync(HttpContext httpContext, string msg)
        {
            ErrorModel error = new ErrorModel
            {
                code = httpContext.Response.StatusCode,
                msg = msg
            };
            var result = JsonConvert.SerializeObject(error);
            httpContext.Response.ContentType = "application/json;charset=utf-8";
            await httpContext.Response.WriteAsync(result).ConfigureAwait(false);
        }
    }

/// <summary>
    /// 中间件拓展类
    /// </summary>
    public static  class MyMiddlewareExtensions
    {
        /// <summary>
        /// 将封装的中间件委托到一个类中，通过IApplicationBuilder拓展方法暴露
        /// </summary>
        /// <param name="builder"></param>
        /// <returns></returns>
        public static IApplicationBuilder UseMyMiddlewareOne(this IApplicationBuilder builder)
        {
            return builder.UseMiddleware<MyMiddleware>();
        }
        /*
         * 下面还可以拓展其他自定义中间件方法，通过IApplicationBuilder暴露
         */
    }

 // 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();
                //开发环境使用
                app.UseSwagger();
                app.UseSwaggerUI(option =>
                {
                    foreach (string version in typeof(ApiVersions).GetEnumNames())
                    {
                        option.SwaggerEndpoint($"/swagger/{version}/swagger.json", $"版本：{version}");
                    }
                });
            }
            app.UseRouting();
            //使用自定义中间件：
            app.UseMyMiddlewareOne();//注册自定义中间件
            app.UseAuthorization();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }

    /// <summary>
        /// 自定义中间件测试
        /// </summary>
        /// <param name="param"></param>
        /// <returns></returns>
        [HttpGet]
        public int  MiddleWareTest(string param)
        {
            /*
             * note:此处的字符串是否是数字不做判断，当输入的非数字字符串时，强转Int服务内部会
             */
            int Number = int.Parse(param);
            return Number;
        }