背景
web上如果圖片不存在一般是打xx，這時候一般都是會設置默認的圖片代替。現在用中間件的方式實現統一設置， 一次設置，全部作用 。
此示例演示如何解決在ASP.NET Core中找不到圖像時設置默認圖像
先決條件
Visual Studio 2017或更高版本。
啓用Visual Studio的ASP.NET Core開發組件。
實現方式
1、Startup 文件
app.UseDefaultImage(defaultImagePath: Configuration.GetSection("defaultImagePath").Value);
2、新建類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 添加路徑
"defaultImagePath": "wwwroot\\DefaultImage.png",
4、最後在wwwroot放張DefaultImage.png圖片即可
開源地址
https://github.com/conanl5566/Sampleproject