Hi Jonathan, Dave
I understand that PRO.narrow is required when casting a (potentially) remote
object reference to cater for using IIOP as the underlying protocol. What I'm
struggling with right now is the requirement of using it on the result of a
multi-object find.
The java typecast used in this case is required purely because a Collection
is not typed. The type of the returned objects is fixed (by contract) to be
an entity object reference of a specific type, that of the bean who's home
interface you are calling findXXX on. I fail to see the difference between
that and the reference returned by a single-object finder. If the returned
Collection was typed (say java supported templates ala C++) there would be
no need for the java cast. Would PRO.narrow be required then and if so, why?
-t
On Wed, Sep 06, 2000 at 04:47:26PM -0700, Jonathan K. Weedon wrote:
> Tony,
>
> The basic rule of thumb is that a PRO.narrow is needed wherever
> a Java cast is needed. Elsewhere, it is not needed.
>
> Specifically, a PRO.narrow IS NOT needed for:
>
> * create methods
> * single object finders (including findByPrimaryKey)
>
> (and you will note a Java cast is also not required).
>
> However, a PRO.narrow is needed for:
>
> * JNDI lookups,
> * multi-object finders (including your findByParent)
>
> (and you will note that a Java cast is required).
>
> The spec is completly consistent on this matter.
>
> -jkw
>
> Tony Abbott wrote:
> >
> > Hi Jonathan,
> >
> > Hmm.. I'd never thought of using PRO.narrow there. Never seen anyone else do
> > it either. Decided to do a little digging and it seems like the spec (1.1 at
> > least) is not entirely clear on this matter. The examples in sections 8.3.1
> > (calling create on home interface) and 8.3.2 (calling findByPrimaryKey) imply
> > that it is not required, since it is explicitly used in the example of 8.2.1
> > (acquiring the home interface) but not in the other two. The examples they
> > use are:
> >
> > 8.2.1
> > Context initialContext = new InitialContext();
> > AccountHome accountHome = (AccountHome) javax.rmi.PortableRemoteObject.narrow(
> > initialContext.lookup( java:comp/env/ejb/accounts ), AccountHome.class);
> >
> > 8.3.1
> > AccountHome accountHome = ...;
> > Account account = accountHome.create( John , Smith , 500.00);
> >
> > 8.3.2
> > AccountHome = ...;
> > Account account = accountHome.findByPrimaryKey( 100-3450-3333 );
> >
> > So to me, these examples seem to make the case against using PRO.narrow on the
> > results of create/findBy*. In my mind this is quite logical, since these are
> > references provided specifically by the container as EJB remote interfaces,
> > whereas the result of lookup() is generic and thus required to be narrow()ed.
> > Surely the container should obviate the need for using PRO.narrow on
> > references that are specifically returned as EJB remote interfaces?
> >
> > BUT then in section 8.9 they go and say
> >
> > "A client program that is intended to be interoperable with all compliant EJB
> > Container implementations must use the
> > javax.rmi.PortableRemoteObject.narrow(...) method to perform type-narrowing of
> > the client-side representations of the home and remote interface."
> >
> > contradicting their examples above.
> >
> > Anyone else have any insight into this? If I'm missing something obvious here
> > please let me know!
> >
> > -t
> >
> > On Wed, Sep 06, 2000 at 01:51:48PM -0700, Jonathan K. Weedon wrote:
> > > Tony Abbott wrote:
> > > >
> > > > findBy methods on the home interface should return either the remote interface
> > > > or a Collection of remote interfaces. So just make findByParent return a
> > > > collection of categories. So your code would look something like...
> > > >
> > > > InitialContext context = new InitialContext();
> > > > Object obj = context.lookup("java:comp/env/ejb/Category");
> > > > CategoryHome ch = (CategoryHome)PortableRemoteObject.narrow(obj,
>CategoryHome.class);
> > > >
> > > > Collection col = ch.findByParent("Furniture");
> > > > Iterator i = col.iterator();
> > > > while (i.hasNext())
> > > > {
> > > > Category cat = (Category)i.next();
> > > > ... do stuff ...
> > > > }
> > > >
> > > > -t
> > >
> > > Tony,
> > >
> > > In the above code, you neglected to use PRO.narrow for the narrowing of
> > > the contents of the Iterator. It should be:
> > >
> > > Collection col = ch.findByParent("Furniture");
> > > Iterator i = col.iterator();
> > > while (i.hasNext()) {
> > > Category cat = (Category) PortableRemoteObject.narrow
> > > (i.next(), Category.class);
> > >
> > > }
> > >
> > > This is one of those insidious cases that I mentioned in a previous
> > > thread, whereby your version of the code would work in some AppServers,
> > > and not in others, even though (given your use of PRO.narrow for the
> > > JNDI lookup) you probably thought you were writing portable code.
> > >
> > > -jkw
> > >
> > > ===========================================================================
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> > >
> >
> > --
> >
> > Tony Abbott [EMAIL PROTECTED]
> >
> > ===========================================================================
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> > [EMAIL PROTECTED] and include in the body of the message "help".
>
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--
Tony Abbott [EMAIL PROTECTED]
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