expiry header : Java Glossary

expiry header

In the header of every HTTP (Hypertext Transfer Protocol) document served is an expiry field. It tells caching software on the net how long this document will remain fresh. If it has a long expiry date, there is a better chance it can be found in a cache somewhere. Then it can be retrieved rapidly without pestering your server. On the other hand, if you change the document, all the old copies is cache won’t be flushed until the expiry date has passed.

If you are sitting at a browser, sometimes hitting Shift-Reload or Ctrl-Reload will force getting a fresh copy.

If you always rename images or zip files when you change them, you can safely give them a very long expiry date, e.g. three months.

Unfortunately you can’t specify the expiry date in your HTML (Hypertext Markup Language). Your ISP (Internet Service Provider) needs to apply the expiry date headers based on some sort of rule such as the Apache rule scheme.

When reading files from a website programmatically, you can force a fresh copy rather a faster cached copy with URLConnection.setUseCaches( false ).

	You can get the freshest copy of this page from:	or possibly from your local J: drive (Java virtual drive/mindprod.com website mirror)
	http://mindprod.com/jgloss/expiryheader.html	J:\mindprod\jgloss\expiryheader.html
	Please email your feedback for publication, letters to the editor, errors, omissions, typos, formatting errors, ambiguities, unclear wording, broken/redirected link reports, suggestions to improve this page or comments to Roedy Green : If you want your message kept confidential, not considered for posting, please explicitly specify that.
	Canadian Mind Products
	mindprod.com IP:[65.110.21.43]
view Blog	Your face IP:[38.107.179.212]
Feedback	You are visitor number 9,911.