The Hibernate classes and the ClassLoader which loads them are not GCed.

The following example has two classes, "CallJunk" creates a ClassLoader , loads Junk and hibernate classes, and call Junk.main(). Junk.main() opens a session and closes it.

The CallJunk program grows 1-2 MB in each loop step and finally run out of memory.
I profiled with JProfiler, found hibernate classes are duplicated, which is loaded by a new URLClassLoader in the Loop, but never GCed.

package calljunk;

import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;

public class CallJunk {

 static String[] dum=new String[0];
 static Class[] parameterTypes = new Class[]{dum.getClass()};

 public static void main(String[] args)throws Exception {
 URL[] urls = new URL[]{
 new File("../junk/cglib-2.1.3.jar").toURL(),
 new File("../junk/commons-collections-2.1.1.jar").toURL(),
 new File("../junk/dom4j-1.6.1.jar").toURL(),
 new File("../junk/ehcache-1.1.jar").toURL(),
 new File("../junk/hibernate3.jar").toURL(),
 new File("../junk/jta.jar").toURL(),
 new File("../junk/postgresql-8.0-311.jdbc3.jar").toURL(),
 new File("../junk/commons-logging.jar").toURL(),
 new File("../junk/bin").toURL()
 };

 for (int i=0; i<100; i++) {
 System.out.println("No "+i+": ");
 System.in.read();
 Class cls = new URLClassLoader(urls).loadClass("junk.Junk");
 cls.getMethod("main", parameterTypes).invoke(null, new Object[]{dum});
 }
 }
}


package junk;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.cfg.Environment;

import javax.naming.InitialContext;

public class Junk {

 private static String CONFIG_FILE_LOCATION = "/hibernate.cfg.xml";

 public static void main(String[] args) throws Exception {
 Configuration cfg = new Configuration();
 SessionFactory sFactory = null;
 try {
 cfg.configure(CONFIG_FILE_LOCATION);
 String sessionFactoryJndiName = cfg.getProperty(Environment.SESSION_FACTORY_NAME);
 if (sessionFactoryJndiName != null) {
 cfg.buildSessionFactory();
 sFactory = (SessionFactory) (new InitialContext()).lookup(sessionFactoryJndiName);
 } else {
 sFactory = cfg.buildSessionFactory();
 }
 } catch (Exception e) {
 throw new HibernateException("Could not initialize the Hibernate configuration");
 }
 Session s = sFactory.getCurrentSession();
 s.close();
 sFactory.close();
 }

}