java，缓存图像不起作用，尽管响应头有max-age

Question

看来这是缓存的：

  

http://agrozoo.net/UploadedImages/d334e86792a547389580a5b5a6a9dcf2_thumb.jpg

而这不是：

  

http://agrozoo.net/UploadedImages/d334e86792a547389580a5b5a6a9dcf2-Phlebia-livida.jpg

从firefox / firebug拍摄的示例屏幕，左缓存，右缓存

在第一种情况下我做的很简单：

chain.doFilter(request, response);

第二名：

response.setContentType("image/jpg");
            OutputStream os = response.getOutputStream();
            ImageIO.write(buffer, "jpg", os);
            os.close();

如何使其在第二种情况下缓存？

Answer 1

左侧和右侧都有Cache-Control: max-age=0标头，将禁用缓存

但左边有一个etag可能会导致缓存

请参阅here以查看可禁用缓存的标头

Answer 2

解决方案：

response.setHeader("ETag", eTag);



if (request.getHeader("If-None-Match") != null && request.getHeader("If-None-Match").equals(eTag))
{        
  response.setStatus(HttpServletResponse.SC_NOT_MODIFIED); // 304
  response.setContentType("image/jpg");
  OutputStream os = response.getOutputStream();
  buffer.flush();//force 0 B jpg image, don't need to send anything as it will be pulled from browser cache
  ImageIO.write(buffer, "jpg", os);
  os.close();
}
else
{    

response.setContentType("image/jpg");
OutputStream os = response.getOutputStream();
ImageIO.write(buffer, "jpg", os);
os.close();
}