目录

背景

先决条件

实现方式

开源地址

背景

web上如果图片不存在一般是打xx，这时候一般都是会设置默认的图片代替。现在用中间件的方式实现统一设置， 一次设置，全部作用 。

此示例演示如何解决在ASP.NET Core中找不到图像时设置默认图像

先决条件

• Visual Studio 2017或更高版本。

• 启用Visual Studio的ASP.NET Core开发组件。

实现方式

1、Startup 文件

app.UseDefaultImage(defaultImagePath: Configuration.GetSection("defaultImagePath").Value);

2、新建类DefaultImageMiddleware

using Microsoft.AspNetCore.Builder;

using Microsoft.AspNetCore.Http;

using System;

using System.Collections.Generic;

using System.IO;

using System.Linq;

using System.Threading.Tasks;

 

namespace conan.Saas.Framework.Middlewares

{

    public class DefaultImageMiddleware

    {

        private readonly RequestDelegate _next;

 

        public static string DefaultImagePath { get; set; }

 

        public DefaultImageMiddleware(RequestDelegate next)

        {

            this._next = next;

        }

 

        public async Task Invoke(HttpContext context)

        {

            await _next(context);

            if (context.Response.StatusCode == 404)

            {

                var contentType = context.Request.Headers["accept"].ToString().ToLower();

                if (contentType.StartsWith("image"))

                {

                    await SetDefaultImage(context);

                }

            }

        }

 

        private async Task SetDefaultImage(HttpContext context)

        {

            try

            {

                string path = Path.Combine(Directory.GetCurrentDirectory(), DefaultImagePath);

 

                FileStream fs = File.OpenRead(path);

                byte[] bytes = new byte[fs.Length];

                await fs.ReadAsync(bytes, 0, bytes.Length);

                //this header is use for browser cache, format like: "Mon, 15 May 2017 07:03:37 GMT".

                //context.Response.Headers.Append("Last-Modified", $"{File.GetLastWriteTimeUtc(path).ToString("ddd, dd MMM yyyy HH:mm:ss")} GMT");

 

                await context.Response.Body.WriteAsync(bytes, 0, bytes.Length);

            }

            catch (Exception ex)

            {

                await context.Response.WriteAsync(ex.Message);

            }

        }

    }

 

    public static class DefaultImageMiddlewareExtensions

    {

        public static IApplicationBuilder UseDefaultImage(this IApplicationBuilder app, string defaultImagePath)

        {

            DefaultImageMiddleware.DefaultImagePath = defaultImagePath;

 

            return app.UseMiddleware<DefaultImageMiddleware>();

        }

    }

}

3、appsettings.json 添加路径

 "defaultImagePath": "wwwroot\\DefaultImage.png",

 4、最后在wwwroot放张DefaultImage.png图片即可

开源地址

https://github.com/conanl5566/Sampleproject