Howdy,
If you're using servlets,
getServletContext().setAttribute("myPersistenceManager",
myPersistenceManager) would do the trick. If you're using JSPs, it's
pageContext.setAttribute(...).
The WeakHashMap is one approach: not one I'd use initially, but only if
you run into issues with a more conservative approach.
Yoav Shapira
Millennium ChemInformatics
>-----Original Message-----
>From: Rob Augustinus [mailto:[EMAIL PROTECTED]
>Sent: Monday, November 24, 2003 2:38 AM
>To: Tomcat Users List
>Subject: Re: shared object cache
>
>
>thanks,
>
>1) That's exactly what I would like to do, but I'm not quite sure how
to do
>this. Could you point me to some documentation?
>
>2) I have thought about the complications of the cache, and indeed I
need
>to
>be carefull. On the other hand though it is not that critical in this
>application.
>
>
>
>Christopher Schultz wrote:
>
>> Rob,
>>
>>> I have written a PersistenceManager class that handles all database
>>> access and uses the SQLData interface to map java objects to
>>> User Defined Types in the oracle database. Every request now
>>> has to create a new instance of the persistencemanager so there is
>>> no sharing whatsoever. I would like the persistencemanager to look
>>> in the object cache first and if the object is not there retrieve it
>>> from the database. I need a way to keep this cache in memory
>>> so all requests can use the same cache.
>>
>>
>> I would do two things:
>>
>> 1) Put your PersistenceManager in the application scope, and re-use
it
>> all the time instead of doing "new PersistenceManager" for every
request.
>>
>> 2) Have your PersistenceManager do its own cachine. One of my
favorite
>> object caching techniques is to simply use a java.util.WeakHashMap.
>> The WeakHashMap works with WeakReferences, so you can fill it with
>> data, and the GC will purge some of it for you if it needs some
memory
>> back.
>>
>> It works just like any other Map, except that you aren't guarenteed
to
>> get your object back, later :)
>>
>> This may sound sketchy, but it's a pretty good cache because it works
>> the same all the time: if you have a cache miss, you go to the
database.
>>
>> Don't forget that caches are complicated: when data changes, you have
>> to make sure that the cache gets updated. If you have multiple
clients
>> and a single database, this gets to be a real nightmare. Only cache
>> things that don't need to be sync'd up-to-the-minute. For those
>> things, *always* go back to the db.
>>
>> -chris
>>
>>
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>
>
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