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From Stephan van Loendersloot <whis...@worldonline.nl>
Subject Re: Tomcat 5.5.12 Refresh/Cache problem
Date Wed, 02 Nov 2005 03:38:49 GMT
Samit Paul wrote:
> Arlene,
> Thanks for the reply. My file is a PNG file. Can you tell me where can I put
> this piece of code.  
> Thanks,
> 
> Samit Paul
> 
> -----Original Message-----
> From: Arlene Milgram [mailto:Arlene.Milgram@MEDecision.com] 
> Sent: Tuesday, November 01, 2005 8:20 AM
> To: users@tomcat.apache.org
> Subject: RE: Tomcat 5.5.12 Refresh/Cache problem
> 
> 
>   /** Turn on caching:  expire in one hour
>    * @param response The Http Response.
>    */
>   public static void setHeadersCacheOn( HttpServletResponse response ){
>     java.util.Calendar expireDate = java.util.Calendar.getInstance();
>     expireDate.add(java.util.Calendar.SECOND, 30 );
>     response.setDateHeader("Expires", expireDate.getTime().getTime()); 
>     response.setHeader("Cache-Control","public,store,cache"); 
>     response.setHeader("Pragma","cache"); 
>   }
> 
> -----Original Message-----
> From: Samit Paul [mailto:spaul@ipcelerate.com] 
> Sent: Monday, October 31, 2005 8:17 PM
> To: users@tomcat.apache.org
> Subject: Tomcat 5.5.12 Refresh/Cache problem
> 
> Can somebody tell me what configuration parameter I need to set to get
> rid
> of page not refreshing.
> I have a png image a.png . When I browse from IE it shows me the image
> properly. Now I put a different image but with the same name a.png.
> Event if I press the browser refresh button , it still does not refresh
> the
> image.

<SNIP>

The problem you describe is on a per-browser-per-user-basis, so they 
will not work effectively.

In IE for example, you can set the caching through the menu Tools -> 
Internet Options -> General and under 'Temporary Internet Files', click 
Settings, then under 'Check for newer versions of stored pages content', 
select 'Every visit to the page'. Also you can set the number of 
megabytes to use for caching to 1Mb.

As said, this totally leaves you up to the visitor's browser settings.

Other suggested options are to add a number of meta-tags or 
response-headers like 'Expires', 'Cache-Control', 
'Pragma->No-Cache->No-Store', 'Cache-Control->pre-check->post-check' to 
your pages.

However, the interpretation of these things, *again* differs per browser 
implementation per user and per HTTP protocol version these things were 
originally designed for.

This has nothing to do with Tomcat or any other webserver.

Some of the meta-tags and response-headers mentioned above even have an 
unreliable effect on the browsers 'Back'-button and on search-engines.

The most reliable way I have found is to simply take Maarten Janssens's 
advice:

<img src="mypicture.jpg?ms=1130901624937">

or even:

<img src="mypicture.jpg?1130901624937">

Where the value '1130901624937' is the current time in milliseconds.

Maybe you didn't understand his reply and you thought something like:

<img src="1130901624937.jpg">

This would indeed leave you with strange duplicate files. The trick is 
to use the time as a parameter appended to the filename, so you can keep 
the name your original image.


HTH,

     --Stephan.

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