Hi!
Bill Petheram wrote:
> In some examples I have seen it is possible for one EJB to do a
> InitialContext.lookup of another EJB as a normal client can. If this is
> valid what is the point of the ejb-ref and ejb-link in the deployment
> descriptor?
In my opinion, it is a huge difference. If you use direct access you are
making the client/bean explicitly aware of where the bean is. If you
change the location of that bean your code will have to be changed. If
you use EJB-references you are using a more declarative approach: "I
want a bean implementing this interface to be bound to this name". And
then you can hardcode to this name everywhere in your bean code, not
really caring about where it is located, but only that it implements the
proper interface. The bean may be in the same application, or it may be
in another application in another server. In the code you don't care,
and this makes your bean less likely to break, and also makes it easier
to adapt it to new situations.
Also, if you port your app to another server the JNDI names that the
beans are bound to may be different (as outlined in previous recent
postings). To make it even worse: there may not even be a JNDI
namespace, since this is not a mandatory thing to have!! Only the java:
namespace is mandatory.
> I ask this because it seems to me that an EJB server cannot be regarded
> as an application server because there are too many restrictions on an
> EJB instance to allow it to represent a large chunk of application. i.e.
> No sockets, thread, file access.
EJB's rarely do system tasks (such as implement a database). They can
use system modules to do that though. An EJB server is not necessarily
an application server, but it can (as jBoss does) allow additional
system modules to be added which may be used by EJB's.
> If this is true I have been thinking about extending a Container or
> adding Resource Factores to provide extra functionality for particular
> types of bean but a bean has a very limited knowledge of it's container
> or container capabilities.
>
> What do othe people think?
Definitely use Resource Factories to do system functionality. Use EJB's
to glue things together into an *appliction*. System modules can usually
be reused for different applications, and do not contain any code that
is specific to the particular application that you are implementing.
/Rickard
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Rickard �berg
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