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Subject: RE: ant tasks creation of classloaders
Date: Mon, 20 Jun 2005 10:03:03 -0700
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Thread-Topic: ant tasks creation of classloaders
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From: "Hyke, Lea" <lhyke@netsuite.com>
To: "Ant Developers List" <dev@ant.apache.org>
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-----Original Message-----
From: Max Rydahl Andersen [mailto:max.andersen@jboss.com]=20
Sent: Saturday, June 18, 2005 2:44 PM
To: dev@ant.apache.org
Subject: ant tasks creation of classloaders

Hi guys,

Having some "fun" issues with classloading these days.

I have a task (HibernateTool) that is used like this:

     <taskdef name=3D"hibernatetool" =20
classname=3D"org.hibernate.tool.ant.HibernateToolTask">
       <classpath path=3D"[necessary hibernate libs]">
     </taskdef>


	<target name=3D"exportddl" depends=3D"compiletest"
description=3D"Export the =20
DDL to caveatemptor.ddl and DB">
         <hibernatetool destdir=3D"${build.dir}">
             <classpath path=3D"etc;${build.dir}/classes"/>
             <annotationconfiguration =20
configurationfile=3D"${classes.dir}/hibernate.cfg.xml"/>
             <hbm2ddl export=3D"false" console=3D"false" drop=3D"false"  =

create=3D"true" outputfilename=3D"caveatemptor.ddl" delimiter=3D";"/>
         </hibernatetool>
	</target>


Notice that the classpath of the taskdef and hibernatetool have no =20
overlaps.

Until today I had the following code in the HibernateToolTask for
creating =20
the classloader:

AntClassLoader loader =3D getProject().createClassLoader(classPath);
loader.setParent(getProject().getCoreLoader());
loader.setThreadContextLoader();

But when I run this stuff with the task above I get ClassNotFoundErrors

for annotations defined in hibernate.

This occurs because with the above classloader setup I effectively goes

around the <taskdef> classpath - it
will instead first look in the parent of the AntClassLoader I created
and =20
this will be the system classloader which
of course know nothing about the hibernate specific classloaders.

Know my current work around for this is to do:

AntClassLoader loader =3D getProject().createClassLoader(classPath);
loader.setParent(this.getClass().getClassLoader()); <-- this is the =20
HibernateToolTask instance
loader.setThreadContextLoader();

This will setup the right classloading sequence.

But i'm just curious of why this does not seem to be the default way of

doing things in the existing ant tasks ?

e.g. in LoadProperties is:
            ClassLoader cL =3D (classpath !=3D null)
                 ? getProject().createClassLoader(classpath)
                 : LoadProperties.class.getClassLoader();

which for me says "ignore LoadProperties own classloader if i have a =20
<classpath>"

and most other places they *only* uses the core task loader which for me

seems kinda strange (as it can give funny
sideeffects if not all classes used by the <taskdef> isn't loaded yet)

So, am I missing some crucial insight or is it just "random" how the =20
current ant tasks setup their classloaders :) ?

Anyone which can think up any bad things with the classloader setup I
did =20
here ?

/max





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