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我开发了一个 http 处理程序来动态提供图像..

我对每个图像都有各自的最后修改日期。

所以我实现了http头缓存，如下：

public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "image/jpeg";

        DateTime lastModified = Convert.ToDateTime("2/1/2013 12:00:00 AM");

        string eTag = "test.JPG" + lastModified.ToString();

        // set cache info
        context.Response.Cache.VaryByHeaders["If-Modified-Since"] = true;
        context.Response.Cache.VaryByHeaders["If-None-Match"] = true;
        context.Response.Cache.SetLastModified(lastModified);
        context.Response.Cache.SetETag(eTag);

        //Set cache control header
        context.Response.Cache.SetCacheability(HttpCacheability.ServerAndPrivate);

        Byte[] imageBytes = CreateImage();
        context.Response.OutputStream.Write(imageBytes, 0, imageBytes.Length);
    }

注意：这里lastModified 将为每个图像动态获取，每个图像的名称也会不同。

响应标头

HTTP/1.1 200 OK
Cache-Control: private
Content-Type: image/jpeg
Last-Modified: Thu, 31 Jan 2013 18:30:00 GMT
Etag: test.JPG2/1/2013 12:00:00 AM
Vary: If-Modified-Since, If-None-Match
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-SourceFiles: =?UTF-8?B?RTpcTGVhcm5pbmdcQ2FjaGVcR2V0SW1hZ2UuYXNoeA==?=
X-Powered-By: ASP.NET
Date: Mon, 08 Jul 2013 11:22:26 GMT
Content-Length: 384411

请求标头

GET /GetImage.ashx HTTP/1.1
Host: localhost:50432
User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:22.0) Gecko/20100101 Firefox/22.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

问题

此页面已正确缓存..但是下次当我加载具有不同 lastModified 值的页面时，这使得 etag 也不同..

但是页面根本没有命中处理程序..它总是显示缓存中的图像......

而且由于它没有击中处理程序，我如何检查 lastModified 值并相应地服务..

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0 回答 0