webstart cache fails to update file

1056969

I've narrowed down a file caching problem we have, where clients that modify files on the server are unable to see these changes within the webstart application.  One server doesn't see the issue.  I have the file http://www-pw.physics.uiowa.edu/~jbf/autoplot/changing/temp.htm which is updated once every minute (with a cron job) and our software that plots this data can see the changes.  The other server, which is updated via svn, doesn't propagate updates when I update the file.  See http://emfisis.physics.uiowa.edu/pub/jy/dev/jbf/20150515_bug1393/temp.htm.

Here are the response headers on the working server, before and after a change:

HTTP/1.1 200 OK

Date: Fri, 15 May 2015 19:51:35 GMT

Server: Apache/2.0.63

Last-Modified: Fri, 15 May 2015 19:51:03 GMT

ETag: "51dc74f-211-2a0297c0"

Accept-Ranges: bytes

Content-Length: 529

Keep-Alive: timeout=15, max=100

Connection: Keep-Alive

Content-Type: text/html

-----

HTTP/1.1 200 OK

Date: Fri, 15 May 2015 20:01:00 GMT

Server: Apache/2.0.63

Last-Modified: Fri, 15 May 2015 20:00:03 GMT

ETag: "51dc74f-20f-4a3256c0"

Accept-Ranges: bytes

Content-Length: 527

Keep-Alive: timeout=15, max=100

Connection: Keep-Alive

Content-Type: text/html

And on the non-working server that doesn't work, before and after the change

HTTP/1.1 200 OK

Date: Fri, 15 May 2015 20:07:20 GMT

Server: Apache/2.4.7 (Ubuntu)

Last-Modified: Fri, 15 May 2015 20:07:02 GMT

ETag: "217-51624632eaaa3"

Accept-Ranges: bytes

Content-Length: 535

Vary: Accept-Encoding

Keep-Alive: timeout=5, max=100

Connection: Keep-Alive

Content-Type: text/html

-----

HTTP/1.1 200 OK

Date: Fri, 15 May 2015 20:09:18 GMT

Server: Apache/2.4.7 (Ubuntu)

Last-Modified: Fri, 15 May 2015 20:09:02 GMT

ETag: "210-516246a5fc440"

Accept-Ranges: bytes

Content-Length: 528

Vary: Accept-Encoding

Keep-Alive: timeout=5, max=100

Connection: Keep-Alive

Content-Type: text/html

Does anyone know why webstart would work fine with one server but not the other?  Is there anything I can do to disable caching in webstart, that would still allow the .jar files to be cached?  I've tried experimenting with this on a single-jar release that doesn't use webstart, and it seems to work fine from both websites.

Thanks,

Jeremy

1056969

Actually on a second machine, neither of the addresses is updating.  So is there a way that the webstart program could programmatically clear the cache, or force a reload?

1056969

I was able to work around this by using the method urlConnection.setUsesCache(false), which I probably want anyway.  I do believe there is a bug in the caching mechanism, and if anyone is capable of addressing it I would be happy to work with them.  It might be worth mentioning that I do a HEAD request before the GET request, so I can manage my own cache, and perhaps this is why no one else has seen the problem.

jlanawalt

Were you able to reproduce the issue when not running under Web Start?

I don't know what your permissions and settings are but while the Web Start sandbox does introduce some differences, DNS lookup caching being a related example, I don't remember URLConnection caching being one of them.

I also wanted more control over caching due to issues with file time stamp being wrong or just not precise enough and trusting the last-modified header over the etag, so I setUsesCache(false) and manage my own header cache along with the downloaded resource. I don't use the HEAD request to do this though. On a 200 response I getHeaderField for a list of headers I care about, loading them into a Properties object then writing that out to a file. When I make the request for the same URL later I load the cached properties and use the Last-Modified value to set the value of the If-Modified-Since header, or if that doesn't exist the ETag value to the If-None-Match. It has seemed to work fine.

--

Jacob