[Cayenne-user] Persistent properties in Tapestry & Cayenne => NPE sometimes

2006/12/18, Øyvind Harboe <[email protected]>:
I'm struggling with a crash in our app and I believe I have understood
what is wrong.


- Using Tomcat
- Marking a Cayenne Data Object as a persistent Tapestry property will
cause it to be put into the servlet session
- Tomcat will then(whenever it feels like it, it seems) serialize my
Cayenne Data Object.
- Serializing a Cayenne Data Object works fine as a Cayenne Data
Object implements Serializable, except that the DataContext is nulled
out.
- Depending on whether or not Tomcat decided to serialize and
deserialize the Cayenne Data Object, I may or may not get an NPE when
trying to do method no the Cayenne Data Object's DataContext (via
getDataContext())

My Servlet superpowers are not quite sufficient to determine the
solution, but a couple of things come to mind:

- Create a non-serializeable wrapper object which has a reference to
the Cayenne Data Object. This will stop Tomcat from trying to
serialize & deserialize my Cayenne Data Objects
- Somehow configure Tomcat not to try to serialize Cayenne Data Objects


If my understanding is correct, then this is *nasty*. The problem is
that this problem does not exist on Jetty(which is our development
environment) and only on certain Tomcat servers depending on
configuration. I prefer being broken all the time instead of
sometimes.

Clustring is an insane overkill for our purposes so I know pffft about
clustering issues.

2006/12/18, Tomi N/A <[email protected]>:

The trick is to be able to attach it to the correct context, if you
have multiple (as you probably do).
Try using the DataContext you store in your session (if that's where
you put it).

On 12/18/06, Tomi N/A wrote:
2006/12/18, Øyvind Harboe <[email protected]>:
You can deserialize cayenne objects, it probably isn't that hard, even
in a container environment. You just extend the CayenneDataObject
class and override the readResolve() method like so:

protected Object readResolve() throws ObjectStreamException {
DataContext dc = ...; // your DataContext, probably in the session
return dc == null ? this : dc.localObject(getObjectId(), this);
}

The trick is to be able to attach it to the correct context, if you
have multiple (as you probably do).
Try using the DataContext you store in your session (if that's where
you put it).

Øyvind Harboe wrote:
Right now I'd like to stop the bleeding by configuring Tomcat not to
try to serialize my persistent Tapestry properties, but that appears
easier said than done....

On 12/18/06, Bryan Lewis wrote:
Øyvind Harboe wrote:
That should be possible. See for example:
http://forum.java.sun.com/thread.jspa?threadID=772735&messageID=4401886

We do that to run with tomcat session persistence disabled. We have no
need for it, no clustering or failover requirements.