I am considering using Castor with JBoss and am trying to work out the most
appropriate architecture for my application. I'm also using Tomcat for a
servlet front end for this app, with Struts MVC architecture and custom JSP
tags. In addition, I'm looking at using EJBDoclet, which I've found does a
very nice job of generating the EJB classes & interfaces. I would
appreciate any thoughts, and in particular, comments from anyone who's
using Castor with JBoss, as to how to best use these technologies together.
Alternatively, please let me know if there are any gotcha's that will make
this technology mix difficult or inadvisable to use.
Here are my questions: (I only have a cursory understanding of Castor at
this point, so please forgive me for any stupid questions):
1. I would like to use Castor to manage persistence of EJB BMP entity
beans, given JAWS' inability at the moment to support dependent objects. An
EJB with no dependent objects would have a single Castor persistent object
associated with it, whereas an EJB with dependent objects would implement
those dependent objects as Castor dependent objects. If I use an
architecture like this, is it best to let Castor directly persist the EJBs,
themselves, or is it better to store the data for an EJB in a separate
Castor data object? Also, for EJB with dependent objects, I assume that
whichever object is chosen as the independent object that Castor persists
for the EJB, that object must maintain references to the dependent objects
for that EJB. Is this correct?
2. I would like to avoid duplicating data objects as much as possible. One
thing that I've noticed with the whole J2EE architecture is that there is a
lot of opportunity to duplicate objects that do roughly, or exactly, the
same thing. For example:
a) Struts uses JavaBeans that extend org.apache.struts.action.ActionForm to
pass data from an HTML form in a JSP to the servlet for processing. In
addition, both these and other, non-ActionForm JavaBeans are used to pass
data back to a JSP for output to the user.
b) It is recommended that data objects be used to pass bulk data between
the EJB client and the EJB in order to minimize network and transaction
overhead. Question: is it a bad idea to use Struts ActionForm beans as
these data objects? The tradeoffs seem to be: if yes, then it increases the
coupling between the EJBs and the front end technology - BAD, but if no,
then it eliminates the need to implement and maintain an additional data
object for the EJB. Opinions?
c) EJB dependent objects - these, too, could theoretically be implemented
by the same JavaBeans used to pass data between JSP pages and servlets. For
example, if a user enters customer information on an HTML form, a JavaBean
could be used to pass the customer's address info to the servlet for
processing (let's call this bean AddressBean). If the Customer EJB has a
dependent object containing the customer address, the AddressBean could be
used not only as a bulk data object to pass the address data to the
Customer EJB, but as the dependent Address object referenced by the
Customer EJB. Again, this increases linkage between the front end and the
back end, but reduces the number of classes that need to be implemented and
maintained. Opinions?
3. Some entity beans will reference other entity beans. AFAICT, JAWS can
automatically manage the persistence relationships between entity beans,
but cannot manage collections of references to other entity beans. I'm
wondering if, and if so, how Castor can be used to manage this sort of
relationship. For example if I have the following EJB entity bean objects:
EntityAEJB
DependentA1 - dependent object of EntityAEJB
DependentA2 - dependent object of EntityAEJB
EntityBEJB
EntityB1EJB extends EntityBEJB - subclass of EntityBEJB
...and EntityAEJB contains a collection of EntityB1EJB objects, can Castor
manage the persistence relationships correctly? I'd use BMP for all entity
beans in this scenario to avoid having to deal with interactions between
Castor and JAWS. What happens if Castor tries to persist EntityAEJB when it
gets to its references to EntityB1? Those references would refer to the
remote interface EntityB1, not EntityB1EJB. Would this work in Castor if
the actual data for these entities is stored in the EJBs themselves? Would
it work if the data for the EJB is stored in a subsidiary Castor data
object? I'm definitely confused about this point...
Thanks for any advice and help,
Rick Horowitz
--------------------
Rick Horowitz
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