Browser Cache: If we change something force user to get new version, not local cached version

We make changes often on our website (which uses caching) and sometimes user don't know to refresh a page in order to get the newest copy of it.

If we do update a开发者_如何学JAVA page, how can we force the users browser to know that there is a new server version, and to use that rather than their browsers cached page?

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Either you can set an http header to force reload every n'th second. That's the easy way, but you probably don't want this. The second way is to use a javascript asking the server via ajax if there is an update. If so, force a reload.

About the cache, you can set an expire header on the page.

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I know the question has been answered, but another way is to set the querystrings at the end of your URL to use a version number:

www.asite.com?version=1.0 //force update
www.asite.com?version=1.1 
www.asite.com?version=1.2 

The browser should request a new cache each time the version number is changed.