JWS, Web Services and Hibernate...

Question

This is design question rather than an implementation question. I am building a web start application that will obtain it's data from web service calls. The web service calls will access the database via hibernate. I'm wondering if other people have done this and how they have solved the issue of passing the hibernate objects across the wire as XML. I wrote a prototype that makes the web service call which accesses the database via hibernate and I created DTO's and used the dozer library to populate the DTO's and pass them across the wire to my JWS client. This seems to work, but is fairly burdensome, in particular maintaining the DTO's and the dozer mapping is tedious as well as the fact that if I don't clip my hibernate object graph dozer will cause hibernate to dereference every relationship in the object graph and pass them all across the wire. Does anyone have a good solution for this problem? Has anyone successfully detached the hibernate objects themselves and passed them directly across the wire to the JWS client? Is there an accepted way of passing the data across the wire? Does anyone know of any white papers on such a subject? Thanks for any information you can provide.

Answer 1

Yes, as part of the jar files that make up the client, I have spring.jar, hibernate.jar, cglib.jar and asm.jar. The spring jar file contains the classes you need in order to call the methods on the server using HTTPInvoker. The hibernate, cglib and asm jar files are needed so that you don't get class not found exceptions when your hibernate enhanced classes are transmitted to the client. Obviously, you also need the same bean classes that you persist on the server to be on the client as well.
The client can then create new beans, modify them, and modify the "hibernate" collections so that when you send them to the server, hibernate will know their dirty state accordingly. All you need to do is get a session in your server method and hibernate will take care of the rest. Here is a snippet of a typical server method in my code that will create or update a Document object coming from the client. It's as simple as that. To return collections is as simple as returning the result of a criteria or hql query.
public Document saveDocument(Document document) throws RepositoryException
    Session session = getSession();
    try
        Date now = new Date();
        if (document.getId() == 0)
            document.setCreated(now);
        document.setLastModified(now);
        session.saveOrUpdate(document);
        return document;
    catch (HibernateException ex)
        throw convertHibernateAccessException(ex);
}You must take care about objects that have references to other objects that are not loaded. If you send them to the client and the client tries to access them, you will get an exception so you must either be aware of this or preload your objects with the related objects that you think you will need on the client. On the server, you don't need to worry about that because hibernate loads them as required (in the same session).
I suggest you read the spring docs on the HttpInvoker. There's a whole chapter on it and it's very easy to use. Just create an interface and an implementation. The client must include this interface so that it knows what methods it can call.
As I mentioned earlier, you need only change a couple of config lines to expose your methods via RMI, SOAP etc.