Re: [Hibernate-devel] mvc & lazy loading

[Jon L. <jon...@xe...>]

Hi All,

I use a Filter (a new addition in the 2.3 servlet spec) to open and close my
Hibernate sessions.  By doing it this way it doesn't matter if I am using
Velocity or JSP or something else to access Hibernate.  As far as the "view"
is concerned the Hibernate session just exists, and only the Filter has to
worry about opening and closing it.

I was looking at the examples inclued with Hibernate and I was thinking that
maybe an example should be added of using a Filter since it's a good way to
cleanly seperate the creation and closing of the sessions for a web
application.

Jon...

PS - Here is a code snippet to get you started if you want to do it this
way:

package example;

import cirrus.hibernate.Datastore;
import cirrus.hibernate.Session;
import cirrus.hibernate.SessionFactory;
import cirrus.hibernate.Hibernate;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class HibernateFilter implements Filter
{
 static org.apache.log4j.Category log =
org.apache.log4j.Category.getInstance(HibernateFilter.class.getName());

 private Datastore datastore;
 private SessionFactory sessions;

 public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException
 {
  try
  {
   // Get the http session id from the request, then we will try to get the
Hiberate
   // Session from the request.  If it doesn't exist, then we will create
it, otherwise
   // we will use the one that already exists.
   String vSessionId =
((HttpServletRequest)request).getSession(true).getId();
   Session vSession = (Session)request.getAttribute(vSessionId);

   if (vSession == null)
   {
    vSession = sessions.openSession();
    request.setAttribute(vSessionId, vSession);

    if (log.isDebugEnabled())
    {
     log.debug("Opened hibernate session.");
    }
   }
  }
  catch (Exception exc)
  {
   log.error("Error opening Hibernate session.", exc);
  }

  try
  {
   chain.doFilter(request, response);
  }
  finally
  {
   try
   {
    String vSessionId = ((HttpServletRequest)request).getSession().getId();
    Session vSession = (Session)request.getAttribute(vSessionId);

    // Only try to close the connection if it is open, since it might have
been
    // closed somewhere else by mistake.
    if (vSession.isOpen())
    {
     vSession.close();

     if (log.isDebugEnabled())
     {
      log.debug("Closed hibernate session.");
     }
    }
   }
   catch (Exception exc)
   {
    log.error("Error closing Hibernate session.", exc);
   }
  }
 }

 public void init(FilterConfig aConfig) throws ServletException
 {
  // Initialize your datastore
  datastore = Hibernate.createDatastore();

  // Initialize your the object -> db mappings
  // ...

  // Initialize your session
  sessions = datastore.buildSessionFactory();
 }

 public void destroy()
 {

 }
}



----- Original Message -----
From: "Christoph Sturm" <ch...@mc...>
To: "Brad Clow" <bra...@wo...>;
<hib...@li...>
Sent: Tuesday, August 27, 2002 10:47 AM
Subject: Re: [Hibernate-devel] mvc & lazy loading


> Hi Brad!
>
> This subject is an interesting one that I was also thinking of lately.
> I did a test app with maverick (mav.sourceforge.net), and there it was
> really easy. If the controller(=model) implements ModelLifetime, a discard
> function is called when the views are finished and the model is discarded.
> There I closed my session. Other frameworks that just forward to the view
> dont offer this functionality.
> For most of my stuff I use webwork, so I'd like a solution that works
there
> too. I was thinking of closing the session in the finalize method of my
> controller, but then I dont really know when the session will be closed.
> Another possibility would be to to pass the session to velocity, and close
> it in the velocity view servlet after all is rendered.
>
> How did you implement it?
>
> regards
>  chris
> ----- Original Message -----
> From: "Brad Clow" <bra...@wo...>
> To: <hib...@li...>
> Sent: Tuesday, August 27, 2002 12:38 AM
> Subject: [Hibernate-devel] mvc & lazy loading
>
>
> >
> > to date, we have avoided using lazy loading when writing a web app in
> > one of the standard mvc type frameworks (eg. struts, webwork, etc).
> > this is because objects r typically retrieved, placed in the request
> > attributes, session closed and control is then passed to the view (JSP,
> > velocity, etc).  if the view attempts to access a lazy loaded collection
> > in one of the objects an exception is thrown as the associated session
> > is closed.
> >
> > what do other people do?
> >
> > yesterday, i spent a few hours writing a very simple webapp framework
> > that uses velocity for the view.  it enables the velocity rendering to
> > be done while a session is open.  so far this is working quite well for
> > us.
> >
> > comments?
> >
> > brad
> >
> > > _______________________________
> > > brad clow
> > > chief technical officer
> > > workingmouse
> > >
> > > email: bra...@wo...
> > > web:   http://www.workingmouse.com
> > >
> >
> >
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