Has anyone tried sending a Hibernate persisted object (with a Set) across a Hessian remote call? It appears that Hibernate's collection classes are not compatible with the way Hessian serializes objects, but I can't believe I'm the only who has tried this (I've done some searches and can't find anyone else mentioning the problem). Yes, the Set is initialized, and no, the persisted object is not a proxy.
This is Hibernate 2.1, btw.

Thanks,
Anodos

There should not be a problem with initialized sets, I think. But yes, the Hessian Serialisation is definately a problem, because Hibernate does a lot of custom serialisation handling. I already had this problem too already. I ended up using http://switchrmi.sourceforge.net/

As it turns out, the solution to using Hibernate with Hessian is to not include the hibernate jar with the client application. The reason is because Hessian treats Collections specially: if an object implements any of the Collection interfaces (List, Set, etc), then Hessian will use the collection accessor methods instead of field level introspection to serialize/deserialize the collection. This means that on the client side, Hessian will create a new Hibernate Set instance, for example, and then call its "add" method in a loop. This results in an exception thrown from Hibernate's Set instance. However, if Hessian cannot find the specific collection instance in the classpath, it will revert to using a default collection instance (HashSet as opposed to Hibernate's Set)... this means that on the client side, all your collections will be standard Java collections instead of Hibernate collections (as long as you do not include the Hibernate jar with your client). Hessian will have essentially "scrubbed" Hibernate off of your data objects.

That is actually nice.

Hm yes, thats nice - it still can't handle uninitialized collections though?

Good question. I don't have any use cases (yet) where I have uninitialized collections by the time I'm serializing them across Hessian. However, since Hessian uses accessor methods (iterators) to deserialize the Collection, then you need to either initialize the collection before sending it across Hessian, or keep your Session open while sending the Collection. The iterator will attempt to initialize the collection, and this will happen on the server side at the point where the collection is serialized via Hessian. Otherwise, I'm sure you'd get a Hibernate exception (on the server side) at the point where the server attempts to transmit the collection.

Not really germane to Hessian, but what the heck: we rolled our own bean serialization on top of XML-RPC (we needed a good, non-RMI way to do service invocations between two apps running on different versions of the JDK, and a little reflection on top of XML-RPC works very well).

For uninitialized collections, our object graph walker just detects the uninitialized state and serializes an empty collection. It also serializes collections generically.

This basically both strips the Hibernate collections from the wire format, and also truncates the object graph at uninitialized lazy collections, which is pretty much exactly what you want.

Cheers!
Rob

Is there any utility clas that can be used to substitute a hibenate lazy loaded collection for a regular one ?

Ie something that traverses the object graph and initializes everything.

It is cool to have lazy loading by default but even cooler if you could just
turn it off whenever you wanted without the overhead of loading the object
and then having to itterate to make it non lazy.

--b

Iterate through all PersistentClass objects in Configuration, set lazy to false and outer-join to false, rebuild the SessionFactory. This will load any referenced instances into memory whenever you load a single entity.

P.S. This is not what you want to happen usually. You are looking for a solution, but probably should rethink the problem.

Hi all, thought this might be of interest to people who are using
hessian. Apparently it's basically the same as hessian but is
more like rmi and will increase hibernate compatability.


http://forum.springframework.org/viewto ... ht=invoker

maybe you should use adifferent protocol which uses java serialization.

e.g. the springframework has some support for that:
org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter
this protocol uses http and java serialization.

RMI should also work.

hey guys,

you made my day!
I also did some prototyping with Spring remoting + Hessian + Hibernate and got stuck with org.hibernate.LazyInitializationException.

The last comment mentioning HttpInvokerServiceExporter did it for me. And it was a simple change of 2 lines in configuration (replacing Hessian).
That is cool!
Thanks.

Really great post, Thank you for sharing This knowledge.Excellently written article, if only all bloggers offered the same level of content as you, the internet would be a much better place. Please keep it up!
------------------------------------
Septorinoplasti