Re: Preventing Parent Classloading

[Upayavira]

Dominique Devienne wrote:
Here's something that might work. The code you sketched below, which only
depends on Cocoon classes, could be make part of Cocoon itself in an
existing or new JAR from Cocoon/WEB-INF/lib, as a new main() entry point.
This way, you could then just use the Java task within your own task (I do
this all the time in my own custom task), calling that entry point, and
setting the classpath explicitly. Play as well with the attributes to
include or not the system and Ant runtime.
 

The only problem I can forsee with this is that I'll already have the 
configuration of the task read into a DOM object, which I'll want to 
pass to the main() method. But I suspect the Java task will only pass 
Strings. Am I correct here?

Regards, Upayavira
Here's some more example code to help. Good luck, --DD
public class JaxbSchemaCompiler extends Task {
   /** The <java> task to run the Jaxb schema compiler. */
   private Java _java;
   // Override Task#init
   public void init() throws BuildException {
       _java = new Java();
       TaskUtils.configureTask(this, _java);
   }
   // Override Task#execute
   public void execute() throws BuildException {
       ...
   }
   ....
}
public class TaskUtils {
   private TaskUtils() {}
    /**
    * Configures a helper task to be used within another task.
    *
    * @param  parent the parent (custom) task using the helper task.
    * @param  helper the helper task to configure for use.
    * @return the configured helper task for call chaining.
    */
   public static Task configureTask(Task parent, Task helper) {
       // Make helper share attributes of the parent
       helper.setProject(parent.getProject());
       helper.setTaskName(parent.getTaskName());
       helper.setOwningTarget(parent.getOwningTarget());
       // Initialize (and return) the helper
       helper.init();
       return helper;
   }
   ...
}
 

-----Original Message-----
From: Upayavira [mailto:[EMAIL PROTECTED]
Sent: Thursday, October 09, 2003 6:00 PM
To: Ant Developers List
Subject: Re: Preventing Parent Classloading
Dominique Devienne wrote:
   

Sounds like the CL you create delegates to the Ant CL, thus your problem.
Create your own CL by making it delegate to the Root/Bootstrap CL (by
setting the parent loader to null), and the classes will always be loaded
     

from your classes (may duplicate-load the some classes Ant loaded in its
CL,
   

but seems alright for you).
     

Firstly, many thanks for your help with the DynamicConfigurator stuff.
It worked a treat.
As to class loading, It is gradually getting worse. I've just realised
that my IDE had included all of the Cocoon classes into the classpath
for Ant, so all of Cocoon's classes were there all along! :-(
As soon as I remove these jars from Ant's classpath, it stops working at
all. So I'm now pretty lost.
All I want to do is this:
In my Task, create a classloader that will ONLY load from
Cocoon/WEB-INF/lib, and then run the following:
       CocoonBean cocoon = new CocoonBean();
       OutputStreamListener listener = new
OutputStreamListener(System.out);
       cocoon.addListener(listener);
       BeanConfigurator.configure(xconf, cocoon, "", uriGroup, listener);
       System.out.println(getProlog(Constants.NAME, Constants.VERSION,
Constants.YEAR));
       cocoon.initialize();
       cocoon.process();
       cocoon.dispose();
       listener.complete();
       return (listener.isSuccessful() ? 0 : 1);
All of the classes mentioned are from Cocoon, none from Ant. Then I'd
switch my classloader back to the Ant one, and I'd be sorted.
Presumably this is a pretty straightforward requirement? Are you able to
suggest places I can look for examples? I've tried looking at the Java
class, but I quickly get out of my depth.
Do I need to load all of my classes using introspection, or can I refer
to them by name as I have above? Do all includes for a class need to be
available to the classloader that loads that class?
   

I'm no class loading expert, but at first glance this should work. --DD
     

I've not even reached beginner level when it comes to class loading I'm
afraid!
Thanks again,
Upayavira
   

-----Original Message-----
From: Upayavira [mailto:[EMAIL PROTECTED]
Sent: Thursday, October 09, 2003 2:39 PM
To: [EMAIL PROTECTED]
Subject: Preventing Parent Classloading
I'm working on a CocoonTask. Cocoon has a significant bundle of jars,
some of which overlap with Ant's.
In my task, I set up a class loader responsible for loading Cocoon
classes, which works, apart from when those same classes exist in Ant,
when the Ant ones are loaded instead of Cocoon's.Ant has a different
version of org.apache.log.Hierarchy which is incompatible with the one
in Cocoon, and thus resulting in an IllegalAccessError.
To quote from the javadocs for ClassLoader:
"When requested to find a class or resource, a ClassLoader instance will
delegate the search for the class or resource to its parent class loader
before attempting to find the class or resource itself. "
How can I reverse this, so that the Cocoon ClassLoader is used in
preference? Or prevent the delegation to the parent class loader?
Thanks in advance.
Regards, Upayavira
       

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