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Data Caching Ideas  RSS feed

 
David Sica
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I'm currently using the Spring Framework, version 1.2.6, for a new application that has a web interface. There are several business/database queries that are very time intensive so I decided to cache this data. The way I implemented this was to create a bean call CacheCleanerJob which contains a List of all the Cache objects. When a new cache is created it registers itself with the CacheCleanerJob.

Because I don't want to keep the cache around indefinitely, the CacheCleanerJob extends org.quartz.Job and runs on a schedule to check each Cache for how long it's been around and if necessary removes the data in the Cache.

I also have a simple JSP page that lists all the Cache's and allows the user to "clean" one or all of the Cache objects on-demand. In addition, there is an interface to the system that allows users to add/delete/modify data that is maintained in the cache. This interface does not directly modify the cache but rather updates the backing database from which the cache is created.

One issue I have with this implementation is that when the Cache is cleared (either on-demand or on a schedule) I'm worried about what will happen if a client is trying the access the Cache at the same time that it is cleared. In fact, in a test cast I've proven in my implementation it's possible (though rare) that if the Cache is cleared at a certain point in time the client will get no data back instead of the "known" result. Also, in some cases I'm getting java.util.ConcurrentModificationException thrown trying to access the Cache objects.

I feel like I'm kind of re-inventing the wheel with this cache implementation and that there may be a better, proven way to implement this functionality to cache data.

I'd really like some feedback on other ideas on how to implement a caching mechanism, either Spring specific or J2EE generic (EJBs?).

Thanks!
David
 
Jesper de Jong
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Yes, there are things like ehcache (I haven't used it myself, but heard the name here and there).

What are you using to access the database - plain JDBC or something like Hibernate? Hibernate has support for ehcache.
 
karl koch
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there are a lot of java cache implentations, ranging from simple to complex. there is definetly no need to implement a cache by yourself.
if you use hibernate to access the DB, then you can transparently plug the cache in (it is called second level cache in hibernate) and enable your objects for caching by modifying the hbm file. if you use some other methods, you might have to do the putting/retrieving from cache yourself:

pseudocode:
public Object getObject() {
Object obj = cache.getObject("foo");
if (obj == null) {
obj = database.getObject("foo");
cache.putObject("foo", obj);
}
return obj;
}


have a nice evening
k
 
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