Hi Kathey,

The approach looks good. More comments below.

On Nov 9, 2005, at 9:14 AM, David W. Van Couvering wrote:

Hi, Kathey.  At first glance it looks good to me.  I'm assuming *all* classes your app needs are available to the from the URL you specify, because you are not specifying a parent classloader when you create it. 

As I understand it, the only classes that need to be available via the special classloader are the Derby implementation classes and its dependencies. JDBC is a pretty good abstraction layer that uses pass-by-value semantics not pass-by-reference semantics, so as long as you're not using user classes inside your database you should be ok.

Also, you'll need to make sure you give the class that runs this code the permission to load classes (I'm not sure exactly how this is done, I just know it's an issue).

You might consider providing a helper class as part of the Derby suite that does have the permission. I think it's RuntimePermission("createClassLoader") permission.

But you might need other permissions as well since you're playing with URLs; e.g., there are file permissions required to read the jar files referenced by the classpath string. 

And you should of course call the privileged methods in a doPrivileged block to avoid the entire call stack from having to have the privilege.

But I am no classloader guru.  I am forwarding this to folks I know within Sun who have done a *lot* of work within classloaders as part of the app server effort.  I'll get back to you with any information I get.


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.
   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)
        // 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)};
            ClassLoader loader1 =new URLClassLoader(urls);
            DataSource ds = newDataSource(loader1,"mydb;create=true");


Craig Russell

Architect, Sun Java Enterprise System http://java.sun.com/products/jdo

408 276-5638 mailto:Craig.Russell@sun.com

P.S. A good JDO? O, Gasp!