Setting HTTP Caching Headers - Cache-Control
The Cache-Control header can be used to expire content
immediately or disable caching altogether. The value of this header
determines whether cached pagelet/portlet content can be shared among
different users.
The Cache-Control header can contain the following values:
| public |
Allows any cached content to be shared across users with identical
sets of preferences using the same portal server. This value should
be used whenever possible. |
| private |
Tells the portal server not to share cached content. The User
ID is added to the cache key so that a separate copy is retained in
the cache for each individual user. This value should only be used
to protect sensitive information, for example, an e-mail inbox portlet.
(User settings can also make public content effectively private.) |
| max-age=[seconds] |
Specifies the maximum amount of time that an object is considered
fresh. Similar to the Expires header, this directive allows more flexibility.
[seconds] is the number of seconds from the time of the request that
the object should remain fresh. |
| must-revalidate |
Tells the cache that it must obey any freshness information
it receives about an object. HTTP allows caches to take liberties
with the freshness of objects; specifying this header tells the cache
to strictly follow your rules. |
| no-cache |
Disables caching completely and overrides Web Service editor
settings. Neither the client nor the Portal Server responds to subsequent
requests with a cached version. |
In JSP, use the setHeader method to configure the Cache-Control
header:
<%
response.setHeader("Cache-Control","public");
%>
The JSP example below expires the content immediately
using the maximum age header.
<%
response.setHeader("Cache-Control","max-age=0");
%>
In .NET, the Cache-Control header is accessed
through the System.Web.HttpCachePolicy class. To set the header to
public, private or no-cache, use the Response.Cache.SetCacheability
method.
Response.Cache.SetCacheability(HttpCacheability.Public);
To set a maximum age for content in .NET, use the Response.Cache.SetMaxAge
method. The example below expires the content immediately.
TimeSpan ts = new TimeSpan(0,0,0);
Response.Cache.SetMaxAge(ts);
To set the header
to must-revalidate in .NET, use the Response.Cache.SetRevalidation
method.
Response.Cache.SetRevalidation(HttpCacheRevalidation.AllCaches);
