如何解决在ASP.NET Core中找不到图像时设置默认图像

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

背景

先决条件

实现方式

开源地址

董川民