asp.net站点 实现图片不存在 返回默认图片

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Web;

namespace imgfilterdemo.App_Code
{
    public class imgHandler : IHttpHandler
    {
        public bool IsReusable
        {
            get { return true; }
        }

        public void ProcessRequest(HttpContext context)
        {
            var path = context.Request.PhysicalPath;
            var patha = context.Request.PhysicalApplicationPath;
            
            if (!File.Exists(path))
            {
                //不存在 则返回默认的图片
                context.Response.WriteFile(patha+ "404.png");
            }
            else
            {
                //图片存在 不做任何处理
                context.Response.WriteFile(path);
            }
            context.Response.ContentType = "image/"+ context.Request.CurrentExecutionFilePathExtension.Replace(".","");
            context.Response.End();
        }
    }
}

1、App_Code目录下新建上述类imgHandler.cs

  2、对应的配置文件

集成模式

 <system.webServer>
    <handlers>
      <add verb="*" name="imgHandler"  type="imgfilterdemo.App_Code.imgHandler" path="*.png"/>
      <add verb="*" name="imgHandler1"  type="imgfilterdemo.App_Code.imgHandler" path="*.gif"/>
      <add verb="*" name="imgHandler2"  type="imgfilterdemo.App_Code.imgHandler" path="*.jpg"/>
      <add verb="*" name="imgHandler3"  type="imgfilterdemo.App_Code.imgHandler" path="*.jpeg"/>
    </handlers>
  </system.webServer>

经典模式

<system.web>  
    <httpHandlers>  
     <add verb="*"  type="imgfilterdemo.App_Code.imgHandler" path="*.png"/>
      <add verb="*"  type="imgfilterdemo.App_Code.imgHandler" path="*.gif"/>
      <add verb="*" type="imgfilterdemo.App_Code.imgHandler" path="*.jpg"/>
      <add verb="*"  type="imgfilterdemo.App_Code.imgHandler" path="*.jpeg"/>
    </httpHandlers>  
  </system.web>