In the HttpServletResponse header what does expire date mean

[Tony Evans]

I am going to write a last-modified header onto a file

HttpServletResponse resp = (HttpServletResponse) response;         
resp.setHeader("Expires", "Tue, 03 Jul 2001 06:00:00 GMT");         
resp.setHeader("Last-Modified", new Date().toString());         
resp.setHeader("Cache-Control", "no-store, no-cache, must-revalidate, max-age=0, post-check=0, pre-check=0");         
resp.setHeader("Pragma", "no-cache");

Found this example, understand all it apart from the Expires, just need to know the significance of the date, so I know what date to set.

Thanks for any Help

[German Gonzalez-Morris]

Those are HTTP headers therefore you must look in the HTTP specification:

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.21
"The Expires entity-header field gives the date/time after which the response is considered stale"

http://en.wikipedia.org/wiki/List_of_HTTP_header_fields#Expires

Cheers,

[Tony Evans]

Thanks Gonzalez-Morris that makes sense so if the date is set in the past the data will always be stale an so every time a file with that header is accesed it will be the latest an not the cache file.