Start with an abstraction definition of a cachinge service

public interface ICachingService
{
   public static String NAME="Aspire.AppObjects.CachingService";
   
   //place the object with a key
   public void cache(Object objectToCache
                     ,String key
                     ,int howLongInTicks);

   //returns null if the key is not there
   public Object getFromCache(String key);

   //For the given key invalidate the object
   public void invalidate(String key);

}

How is this used?

public class RequestBasedMasterPagePart
{
   protected IMasterPage create(String requestName, Map params)
          throws RequestExecutionException
   {
      //Get it from the cache
      Object obj = CacheUtils.getObjectFromCache(requestName, params);
      if (obj != null)
      {
         //Object is in the cache
         return (IMasterPage)obj;
      }

      //some how get the master page
         
      //Place the object in cache
      CacheUtils.putObjectInCache(requestName, params,masterPage);
      return masterPage;
     
   }//eof-function
}//eof-class   

Where is the cache key then

request.GetMasterPage.classname=com.ai.masterpage.RequestBasedMasterPagePart
request.GetMasterPage.masterPageTemplateRN=GetMasterPageTemplate
request.GetMasterPage.cacheKey=/{ownerUserId}/masterpage

The CacheUtils will just figure out the key from the request name, which in this case is "GetMasterPage". In other words, the CacheUtils can cache an object based on its request name and parameters in turn deriving the cache key from those. Using this pattern we can enable any request centric object for caching based on parameters. For example we can cache this object per user or any other parameter if that is needed.

Invalidating the cached master page using a declarative caching part

request.UpdateMasterPage.classname=com.ai.db.DBPreTranslateArgsMultiRequestExecutor
request.UpdateMasterPage.db=reportsdb
request.UpdateMasterPage.query_type=update
request.UpdateMasterPage.request.1=UMP.checkItemID
request.UpdateMasterPage.request.2=UpdateMasterPage1
request.UpdateMasterPage.request.3=InvalidateMasterPageCache

Caching part defined

request.invalidateMasterPageCache.classname=com.ai.cache.InvalidateCachePart
request.invalidateMasterPageCache.cacheKey=/{profile_user}/masterpage

A possible Caching service implementation

 public class DefaultCachingService implements ICachingService
{

   //
   Hashtable ht = new Hashtable();

   //**************************************************************************
   //place the object with a key
   //**************************************************************************
   public void cache(Object objectToCache
                     ,String key
                     ,int howLongInTicks)
   {
      CacheableEntity ce = new CacheableEntity(objectToCache,key,howLongInTicks);
      ht.put(key,ce);
   }

   //**************************************************************************
   //returns null if the key is not there
   //**************************************************************************

   public Object getFromCache(String key)
   {
      CacheableEntity ce = (CacheableEntity)ht.get(key);
      if (ce == null)
      {
         AppObjects.log("Info: Requested cached object for key:" + key 
             + " is not in the cache.");
         return null;
      }
      return ce.m_cachedObject;
   }

   //**************************************************************************
   //For the given key invalidate the object
   //**************************************************************************
   public void invalidate(String key)
   {
      CacheableEntity ce = (CacheableEntity)ht.get(key);
      if (ce == null)
      {
         AppObjects.log("Warn: Requested cached object for key:" + key 
             + " is not in the cache for invalidation");
         return;
      }
      //Ce is there. Remove it from the cache
      AppObjects.log("Info: Cached object with key:" + key 
           + " is being removed from the cache");
      ht.remove(key);
   }
}//eof-class

//**************************************************************************
//* Local CacheableEntity class
//**************************************************************************
class CacheableEntity
{
   public Object m_cachedObject;
   public String m_key;
   public int m_ticks;

   public CacheableEntity(Object inObject, String inKey, int inTicks)
   {
      m_cachedObject = inObject;
      m_key = inKey;
      m_ticks = inTicks;
   }
}

References

1. General Introduction to other Server side Patterns in this series

2. OSCON 2004 Summary page for Server side patterns session

3. Master Pages Pattern: Code Examples.