Using the BusinessDelegate pattern at lower levels

I was hoping to elicit some feedback on general J2EE architecture...
We have an application that we separate into three general tiers: web/client tier, service tier (with 'services' that implement business logic) and a data tier (with 'controllers' which basically implement CRUD (create, read, update, delete) for a single domain object or table). We have this thing called a 'manager' that straddles the service and data tier which also implements CRUD, but at a more coarse grained level. Managers allow us to work with big objects that are actually a composition of small objects.
Our services and managers are almost always implemented as session beans (stateless) so the client tier uses a "Business Delegate" as per Sun's J2EE patterns to hide the implementation details of those services and managers. So a given call in the system would look like:
Struts action class -> business delegate -> manager or service -> controller -> entity bean
Managers and services, when they need to work with persistent data then use controllers to get at that data. Most controllers are currently session beans (stateless), but we are starting to add controllers that implement the DAO pattern.
I'd like to hide the implementation details of those controllers from the managers and services that use them, though. I hate seeing code in managers/services where we use ServiceLocator to look up a home interface, create the EJB controller and then do method calls.
My question is whether it's possible and appropriate to use a BusinessDelegate between two session beans such as our 'managers' and 'controllers'. Doing so would make a given call in the system would look like:
Struts action class -> business delegate -> manager or service -> business delegate -> controller -> entity bean (if used). Would you loose the transaction between manager and controllers (managers always use Required for each method and controllers use Supports - as well, controllers only ever expose a local interface).
Thanks for any advise/opinions you might have.
Donald

In your framework, does each delegate become a single
InvocationHandler instance
Yes, exactly.
with (for instance) a
constructor that does the EJB lookup and an invoke()
method?
EJB lookup is being done by a ServiceLocator.
Do you have ServiceLocator return the proxy object (I
know that traditionally ServiceLocators merely return
EJB home interfaces,
My does the same. But it's used by EJBDelegateFactory, which creates EJBDelegates.
EJBDelegates implement InvocationHandler and support InvocationDecorators.
but I have used them to return
POJO implementations of interfaces so it becomes a
kind of implementation factory).
Nice idea. I have POJOLocator for that.
Do you have your Proxy object implement the EJB
interface, rather than creating a new one.
Yes. The only drawback is that client code needs to catch EJB specific and remote exceptions.
However it's not a big problem, because there is a decorator which catches all EJB exceptions and throws BusinessDelegateException with a user-friendly error message inside. This means that EJB interfaces need to declare BusinessDelegateException in throws clauses, but it doesnt cause any problems.
So client code is something like:
try {
      foo.invokeSomeMethod();
} catch (BusinessDelegateException ex)
     displayErrorMessage(ex.getMsg);
}   catch (Exception ex)
      //   can be empty
I have
been thinking about creating a new one and then seeing
if I can change xdoclet's templates to have the EJB
interface extend this interface.
I have used this idea, too. I think it's even called a pattern. You can make EJB bean to implement this interface and then you have compile time checking of EJB compliance.
I remember I had problems with that when some CORBA client stub generator got confused.
Thanks for any little advise you can provide.
Maybe I will even put my framework as OS in WEB. If my client will allow me to do it.
best regards,
Maris Orbidans

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"Matt361" <[email protected]> wrote in message news:[email protected]..
Hi,
 
I'm trying to use the mattch pattern function to find the first string in a table thats is >0. My table looks like:
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