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