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Date: Fri, 11 Nov 2005 15:21:06 -0800
From: "David W. Van Couvering" <David.Vancouvering@Sun.COM>
Subject: Re: Question about using URLClassLoader and Derby
In-reply-to: <43722A1E.4000402@sbcglobal.net>
To: Derby Discussion <derby-user@db.apache.org>, Binod P G <Binod.Pg@Sun.COM>
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Here's an answer from Binod, one of our app server engineers...

Kathey Marsden wrote:
> My goal is:
> I want to use a specific version of Derby which I ship with my app and I
> don't  want to interfere with any other derby versions loaded  in the
> same JVM or have them interfere with me.   I am creating a new
> datasource in a separate URLClassLoader and using that for creating all
> my connections.  Are there other things I need to do to meet my goal?  
> I have a feeling it all must be more complex than it looks to me right now.
> 
> Thanks
> 
> Kathey
>    
> Below is some code showing what I have done in playing with this  so far.
> 
> Method to load derby in separate loader and create datasource:
>       
>       private static DataSource newDataSource(ClassLoader loader, String
> databaseName) throws Exception
>     {
>         DataSource ds = (DataSource)
> loader.loadClass("org.apache.derby.jdbc.EmbeddedDataSource").newInstance();
>         // setDatabaseName with reflection
>         Class[] argType = {String.class};
>         String[] args = new String[] {databaseName};
>         Method sh = ds.getClass().getMethod("setDatabaseName", argType);
>         sh.invoke(ds, args);
>         return ds;
>        
>     }
> 
>     // Calling program ....
>     .....
>         URL[] urls =
>                   new URL[]{new URL(derbyJarURLString)};
>             System.out.println(urls[0].getFile());
>             ClassLoader loader1 =new URLClassLoader(urls);
>             DataSource ds = newDataSource(loader1,"mydb;create=true");
>             ds.getConnection();
>    ...
> 
> 
> 

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Date: Fri, 11 Nov 2005 16:57:53 +0530
From: Binod P G <Binod.Pg@Sun.COM>
Subject: Re: [Fwd: Question about using URLClassLoader and Derby]
In-reply-to: <43723003.3090506@sun.com>
To: "David W. Van Couvering" <David.Vancouvering@Sun.COM>
Cc: "Lance J. Andersen" <Lance.Andersen@Sun.COM>,
 Amit Handa <Amit.Handa@Sun.COM>, Craig Russell <Craig.Russell@Sun.COM>
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David W. Van Couvering wrote On 11/09/05 10:51 PM,:
> Hi, guys.  Is there any helpful information you can provide Kathey?  You 
> can respond to me or directly to derby-user@db.apache.org.  If you load 
> one class with a classloader, will all other classes for objects created 
> by that class be loaded from the same classloader?  If not, how do you 
> achieve what she is trying to accomplish?

Make sure that there is only one URL classloader instance that has
access to the derby jar files. And make sure that whenever a code
accesses the datasource, it always go thru newDataSource method, then
yes, it should work.

- Binod.

p.s: This is all assuming that derby code doent do any other interesting
classloader mechanism inside :-). For example, it can use Thread's
context classLoader to load some other part of derby that might break.


> 
> Thanks!
> 
> David
> 
> 
> ------------------------------------------------------------------------
> 
> Subject:
> Question about using URLClassLoader and Derby
> From:
> Kathey Marsden <kmarsdenderby@sbcglobal.net>
> Date:
> Wed, 09 Nov 2005 08:55:58 -0800
> To:
> Derby Discussion <derby-user@db.apache.org>
> 
> 
> My goal is:
> I want to use a specific version of Derby which I ship with my app and I
> don't  want to interfere with any other derby versions loaded  in the
> same JVM or have them interfere with me.   I am creating a new
> datasource in a separate URLClassLoader and using that for creating all
> my connections.  Are there other things I need to do to meet my goal?  
> I have a feeling it all must be more complex than it looks to me right now.
> 
> Thanks
> 
> Kathey
>    
> Below is some code showing what I have done in playing with this  so far.
> 
> Method to load derby in separate loader and create datasource:
>       
>       private static DataSource newDataSource(ClassLoader loader, String
> databaseName) throws Exception
>     {
>         DataSource ds = (DataSource)
> loader.loadClass("org.apache.derby.jdbc.EmbeddedDataSource").newInstance();
>         // setDatabaseName with reflection
>         Class[] argType = {String.class};
>         String[] args = new String[] {databaseName};
>         Method sh = ds.getClass().getMethod("setDatabaseName", argType);
>         sh.invoke(ds, args);
>         return ds;
>        
>     }
> 
>     // Calling program ....
>     .....
>         URL[] urls =
>                   new URL[]{new URL(derbyJarURLString)};
>             System.out.println(urls[0].getFile());
>             ClassLoader loader1 =new URLClassLoader(urls);
>             DataSource ds = newDataSource(loader1,"mydb;create=true");
>             ds.getConnection();
>    ...
> 
> 
> 

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