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From Daniel John Debrunner <...@apache.org>
Subject Re: Derby storage using Java Web Start PersistenceService API - is it doable?
Date Sat, 17 Mar 2007 15:07:39 GMT
David Van Couvering wrote:
> Hi, Luigi.  I looked at this once, and it really didn't seem that the 
> API provided by the JWS persistence service was sufficient for the needs 
> of Derby.  But I didn't look too closely at it.  For me demo needs, a 
> popup was fine.
> 
> What you'd have to do is provide a new implementation of the storage 
> interface.  Others on this list can give you better guidance than I 
> about where to look and how to do this.  I suspect this is not for the 
> faint of heart...

As Andrew pointed out this is would be an implementation of 
org.apache.derby.io.StorageFactory against Java Web Start 
PersistenceService API.

The StorageFactory is is an abstraction around the java filesystem 
classes so in theory it's not hard to understand. All of the database 
specific internals are above this layer and would not need to be 
changed. It's much like the Directory abstraction in Apache Lucene Java.

You can find the internals java doc at

http://db.apache.org/derby/javadoc/engine/

then look for the org.apache.derby.io package.

Here's some information on getting involved in Derby's development:

  http://wiki.apache.org/db-derby/DerbyDev

I would encourage you to subscribe to derby-dev and involve the 
development community in implementing this (asking questions, 
incremental development etc.).

The in-memory implementation Andrew references may not be the best model 
to follow, the implementation seems to add new api classes with no 
indication of what their functionality is required to be, i.e. no 
comments. Then the original contributor never responded to any questions 
and non-one else has had the itch to pick up the code. Thus that 
implementation has stalled and not been committed. It would be a shame 
for any Java Web Start PersistenceService implementation to go the same way.

In the Derby code there are three implementations of StorageFactory that 
are in use, for file system, jar files and classpath. There is one more 
that is not in use, fetching data from an http server. Look for 
subclasses of StorageFactory.

HTH,
Dan.


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