JRE Cache ignores the "Expire" and "Cache-Control: no-cache" directives.

Question

My applet is using HttpURLConection to retrieve data from a server with Caching enabled. The cache contents are "revalidated" (via "if-modfied-since") each time the applet is started. However, subsequent requests to retrieve the same resource are always read from the cache with no validation even if the resource has expired.
The server is sending a valid "Expires:" tag and "Cache-Control: no-cache" tag in the response; but, the JRE refuses to recheck for an updated version of the resource even after the file has expired.
The JRE does seem to understand the "Cache-Control: no-store" tag; but, this is inefficient (no caching at all) when I'm tring to get it to not refetch the resource unless there's a change. Is there some other tag that the JRE is expecting to see?

Answer 1

I have a similar problem except that I want my pages to not cache at all. The server is setting the Cache-Control: max-age to 0 and the Expires to "now" but JRE seems to ignore these settings, but only sometimes. Sometimes pages are fetched from cache and sometimes from the server.
In my applet I'm using a normal URLConnection like this:
URLConnection uc = new URL("http://<server>/method").openConnection();
uc.connect();
InputStream is = uc.getInputStream();
is.read();When my request headers look like this:
accept-encoding: gzip
Host: <server>
Cache-Control: no-cache
Pragma: no-cache
User-Agent: Mozilla/4.0 (Windows XP 5.1) Java/1.6.0_13
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
Connection: keep-alivethe page will not be cached and is requested again but this time without the accept-encoding, Pragma and Cache-Control. The adding (and removal) of the headers seems to happen inside the JRE, though. I'm not explicitly setting them.
The response header of the first request looks like this:
HTTP/1.1 200 OK
Date: Wed, 20 May 2009 12:55:07 GMT
Server: Apache/2.2.11 (Win32) mod_jk/1.2.26 PHP/5.2.8
Cache-Control: max-age=0
Expires: Wed, 20 May 2009 12:55:07 GMT
Vary: User-Agent,Accept-Encoding
Content-Encoding: gzip
Keep-Alive: timeout=120, max=79
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html;charset=iso-8859-1When the request is made with this header:
User-Agent: Mozilla/4.0 (Windows XP 5.1) Java/1.6.0_13
Host: <server>
Accept: text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2
Connection: keep-aliveThe response headers looks like this:
HTTP/1.1 200 OK
Date: Wed, 20 May 2009 12:55:07 GMT
Server: Apache/2.2.11 (Win32) mod_jk/1.2.26 PHP/5.2.8
Content-Length: 1016
Cache-Control: max-age=0
Expires: Wed, 20 May 2009 12:55:07 GMT
Vary: User-Agent,Accept-Encoding
Keep-Alive: timeout=120, max=83
Connection: Keep-Alive
Content-Type: text/html;charset=iso-8859-1And in this case the JRE sometimes fetches the request from the server and sometimes from cache. I have not been able to determine how the JRE decides to refresh, or why it sometimes sends an accept-encoding and Pragma header and sometimes not.
any help would be appreciated.
Alex