The main drawback of using a global cache (and even Servlet sessions) to store user-specific data, is it that the developer must carefully create a key to associate with the cached item. The key should be unique for the user as well as the browser window that is associated with the item that is being stored (in our application we discovered collisions when there were multiple windows used by one user to access the same screen). A timestamp should suffice to avoid conflicts between a user's multiple sessions, which can be combined with a user id, to generate an id that is unique to both the user and the screen.
These pitfalls can be avoided by passing the data in the URL, but that can be inconvenient or impractical if there is a lot of information, such as lots of form fields, or if it really makes sense to use objects.
Nate
Greg Kerdemelidis wrote:
Ahh, very true. There is a built-in GlobalCache service in Turbine (2.2, at least) which may be useful to you (it supports expiration but not to disk, etc). I guess it depends what you need it for.
Global caches can have some drawbacks when you want data tied to a particular session...
If you decide to use the GlobalCache service, you might find these static accessors handy:
----------- package com.genix.property.utils;
import org.apache.turbine.services.TurbineServices; import org.apache.turbine.services.cache.CachedObject; import org.apache.turbine.services.cache.GlobalCacheService; import org.apache.turbine.services.cache.ObjectExpiredException;
/**
* Static accessors to the turbine GlobalCacheService.
* * @author Greg Kerdemelidis (greg at genixsystems dot com)
*/
public class CacheUtils
{
/**
* Get an object from the Turbine global cache service.
* * @param key The key for the desired object.
* @return Object that was stuffed into the cache.
* @throws ObjectExpiredException when the Object has expired, or
does not exist.
* @throws InstantiationException when the GlobalCacheService cannot
be located.
*/
public static Object get(String key)
throws ObjectExpiredException, InstantiationException
{
/*
* Look for the item in the cache.
* If it doesn't exist or the item is stale,
* the cache will throw an exception.
*/
GlobalCacheService gs =
(GlobalCacheService)TurbineServices.getInstance().getService(
GlobalCacheService.SERVICE_NAME);
return gs.getObject(key).getContents(); }
/**
* Puts an object in the Turbine global cache.
* * @param key The key for the data.
* @param o The data.
* @param duration How long before the data gets expired (in
milliseconds)
* @throws InstantiationException when the GlobalCacheService cannot
be located.
*/
public static void put(String key, Object o, long duration)
throws InstantiationException
{
GlobalCacheService gs =
(GlobalCacheService)TurbineServices.getInstance().getService(GlobalCacheServ
ice.SERVICE_NAME);
gs.addObject(key,new CachedObject(o,duration));
}
}
-----------
-----Original Message----- From: Nathaniel Reed [mailto:[EMAIL PROTECTED] Sent: Thursday, 30 October 2003 11:33 a.m. To: Turbine Users List; [EMAIL PROTECTED] Subject: Re: persisting objects in context across requests
Hi, you might be interested in a technique we borrowed from a JavaWorld article:
http://www.javaworld.com/javaworld/jw-06-1999/jw-06-cooltools.html
It's a "cache" that can be used to conveniently store objects in-between HTTP requests. We easily extended this caching mechanism to write out the objects to disk when they expire, and to retrieve them from disk if they are not in the cache.
Nate
brian wrote:
Hello,---------------------------------------------------------------------
Is there a way to save an object in the (org.apache.velocity.context.Context) for longer than the current page request, so it may retrieved from a different template page later?
Brian A
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