Hibernate objects and GWT-RPC

Question

I want to transfer hibernate objects with GWT-RPC to the frontend. Of course i can not transfer the annotated class because the annotations can not be compiled to javascript. So i did the hibernate mapping purely in the ".hbm.xml". This worked fine for very simple objects. But as soon as i add more complex things like a oneToMany relationship realized with e.g. a set, the compiler complains about some serialization issues with the set (But the objects in the set are serializable as well).

I guess it does't work because hibernate creates some kind of special set that can not be interpreted by GWT?

Is there any way to get around this or do i need another approach to get my objects to the frontend?

Edit: It seems that my approach is not possible with RPC because hibernate changes the objects. (see answer from thanos). There is a newer approach from google to transfer objects to the the frontend: The request factory. It looks really good and i will try this now.

Edit2: Request factory works perfectly and is much more convenient than RPC!

Answer 1

This is a quote from GWT documentation. It says that hibernate changes the object from the original form in order to make it persistent.

What this means for GWT RPC is that by the time the object is ready to be transferred over the wire, it actually isn't the same object that the compiler thought was going to be transferred, so when trying to deserialize, the GWT RPC mechanism no longer knows what the type is and refuses to deserialize it.

Unfortunately the only way to implement the solution is by making DTOs and their appropriate converters.

Using Gilead is a cleaner approach (no need for all this DTO code), but DTOs are more ligtweight and thus produce less traffic through the wire.

Anyhow there is also Dozer, that will generate the DTOs for you so there will not be much need for yo to actually write the code.

Either way as mchq08 said the link he provided will solve many of questions.

I would also make another suggestion! Separate the projects. Create a new one as a model for your application and include the jar into the GWT. In this way your GWT project will be almost in its' entirety the GUI and the jar library can be re-used for other projects too.

Answer 2

When I created my RPC to Hibernate I used this example as a framework. I would recommend downloading their source code and reading the section called "Integration Strategies" since I felt the "Basic" section did not justify DTO. One thing this tutorial did not go over as well is the receiving and sending part from the web page(which converts to JS) so thats why I am recommending you downloading their source code and looking at how they send/receive each the DTOs.

Post the stack trace and some code that you believe will be useful to solving this error.

Google's GWT & Hibernate

Reading this (and the source code) can take some time but really helps understands their logic.

Answer 3

I used the next approatch: for each hibernate entity class I had client replica without any hibernate stuff. Also I had mechanism for copy data between client <-> server clases. This was working, but I belive current GWT version should work with hibernate-annotated classes..

Answer 4

On a client project, I use Moo (which I wrote) to translate Hibernate-enhanced domain objects into DTOs relatively painlessly.