We all know that open a sessionFactory and reading a property file or hibernate.cfg.xml takes time. This should not be done for each query/update request coming from the web client. But what is the best way to do it? At webserver startup time and then cache it? Any suggestions would be highly appreciated.

First chapter, reference documentation.

You can do the configuring once in a class like this one.
When you need a session call

session = SessionHelper.openSession();

package com.rhi.bob.common.dao.impl.hibernate;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import net.sf.hibernate.HibernateException;
import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.cfg.Configuration;

public class SessionHelper {

private static SessionFactory sessionFactory;
protected static Log log = LogFactory.getLog(SessionHelper.class);

static {
try {
Configuration conf = new Configuration();
conf.configure(); // to load default "hibernate.cfg.xml"
sessionFactory = conf.buildSessionFactory();
} catch (HibernateException he) {
String[] msgs = he.getMessages();
for ( int i = 0 ; i < msgs.length ; i++ ) {
log.error(msgs[i]);
}
he.printStackTrace();
}
}

public synchronized static Session openSession() throws HibernateException {
return sessionFactory.openSession();
}

public synchronized static void close(Session session) {
if(session == null) {
return;
}

try {
session.close(); // disconnect session
} catch(Exception e) {
e.printStackTrace();
log.error("failed to commit a session: " + e);
}
}
}

This class is broken (it swallows exceptions). Please, use the one from the Hibernate reference documentation, not one from a very bad book.

you could look into Spring. it has built in DAO Support for Hibernate as well as JDBC based DAOs and does a great job.

if you go with spring, be sure to do it not only for a sessionFactory singleton!

download caveatemptor and just use hibernatefilter and hibernateutil classes, easy ;)

i just downloaded the source code for caveatemptor to look at the use of HibernateUtil. i noticed that you are using HibernateFilter to commit transactions and close the HibernateSession, which is a nifty trick to manage the session per request type of DAO architecture.

however, i do have a conceptual question and maybe someone can help me out with this. i usually build my applications using filters as the layer that sits between the user and the request in order to "filter" the request to the appropriate transition state. the caveatemptor style of architecture has the filter as a layer that sits between the application and the response. i do not doubt one bit that it works exactly as advertised. but isn't it an unconventional use of Filters.

i am sure some of this thought process is due to my preconceived notions about the use of filters. i would appreciate it if any of the "forerunners" (sorry, playing too much halo2) could help with a conceptual explanation of this utilization of filters. also, how would the application work if the user terminated the session before the response could be sent back to the browser? would that keep the session open pending GC?

Uhm, try Hibernate in Action :)

i probably should get a copy anyway. :)

but i was hoping for a brief synopsis on this particular question. it is just that i get a bit nervous keeping database sesssion related stuff so close to the end points of the application i.e. next to the request/response.