出于某种原因，JSF不会在PNG文件上设置标题，但它会在JPG文件上设置标题。 例如https://www.medexpress.co.uk/
所有图片均使用graphicImage。 e.g。
<h:graphicImage library="img" name="logos/medexpress-logo.png" alt="MedExpress UK" />
logos.jpg.xhtml？ln = img（不丢失缓存标头）
Content-Encoding:gzip
Content-Length:7694
Content-Type:image/jpeg
Date:Mon, 11 Jan 2016 01:22:50 GMT
ETag:W/"7890-1448193800000"
Expires:Wed, 17 Feb 2016 08:11:29 GMT
Last-Modified:Sun, 22 Nov 2015 12:03:20 GMT
Vary:Accept-Encoding
medexpress.png.xhtml？ln = img（缺少缓存标头）
Connection:Keep-Alive
Date:Mon, 11 Jan 2016 01:31:17 GMT
Keep-Alive:timeout=5, max=99
Vary:Accept-Encoding