[jboss-as7-dev] PART 3! of EJB Remote client design

[David M. Lloyd]

On 09/22/2011 08:59 AM, Carlo de Wolf wrote:
> On 09/22/2011 03:21 PM, David M. Lloyd wrote:
>> On 09/22/2011 03:52 AM, Carlo de Wolf wrote:
>>> On 09/22/2011 07:00 AM, David M. Lloyd wrote:
>>>> Client JNDI Revisited!
>>>> ----------------------
>>>>
>>>> Based on feedback here and in IRC, we're changing our approach to
>>>> client
>>>> EJB thus:
>>>>
>>>> A new JNDI "scheme" will be introduced called "ejb". Lookups into this
>>>> scheme following a naming convention will yield remote EJB proxies
>>>> directly. If the interface is not stateful, then the proxy is
>>>> immediately available without a server round-trip.
>>>>
>>>> The format for "ejb" scheme names is like this (square brackets are not
>>>> literal; they indicate that the enclosed section is optional):
>>>>
>>>> "ejb:appname/modulename/[distinctname/]beanname!interface[?stateful]"
>>>>
>>>> The "appname", "modulename", and "distinctname" are the identifying
>>>> names of the EJB deployment. "beanname" is the EJB-spec name of the
>>>> EJB. "interface" is the Java type name of the interface being returned.
>>>> The "?stateful" query parameter indicates that a session should be
>>>> initiated on lookup.
>>>>
>>>> Since it is likely that users will erroneously use "?stateful" on a
>>>> stateful home interface (which is itself stateless), the lookup code
>>>> will detect whether the interface extends EJBHome before attempting to
>>>> initiate session, and if found will instead emit a warning.
>>>
>>> Both a SLSB and a SFSB can have an EJBHome interface for their remote
>>> home view. So I don't see how this can play a role in determining the
>>> session characteristic.
>>>
>>> In fact a call to a home view is always session-less, both for SLSB and
>>> SFSB. The proxy returned by the create method represents the possible
>>> session.
>>
>> That's what I said. EJBHome are always stateless. Therefore if
>> ?stateful is given for an EJBHome, it is ignored and a warning is issued.
>
> That implies that home.create() will always go round trip. Isn't that
> what we want to prevent for SLSB?

Yeah I wanted to prevent that but given that (a) it's considerable added 
complexity (we'd need another proxy type) and (b) it's one edge case of 
EJB2-style stuff that hopefully is less-used, it doesn't really seem 
worth the trouble.

>>>> This gives us configuration-free JNDI. Also, it gives us a JNDI name
>>>> scheme we can use in server-side EJB references as a lookup-name which
>>>> can create dependency-free injections of remote EJBs that may not be
>>>> present on the current system. And it's also nice in that it doesn't
>>>> interfere with "java:" spec lookups at all.
>>>>
>>>> This should address all the issues raised with client JNDI thus far.
>>>
>>> Binding the URL ObjectFactory to java:something would result in exactly
>>> the same functionality. We can still offer this choice to users.
>>
>> Except that "java:" belongs to EE, and this is very much non-spec. I
>> don't think this type of functionality belongs in "java:" under any
>> circumstances.
>
> In that case we should also refactor java:jboss.

The reason I don't feel "java:jboss" applies the same way as "ejb:" is 
that (a) it is very unlikely to conflict, given that "jboss" is 
basically trademarked, and (b) it behaves very similarly to other 
"java:" namespaces.


-- 
- DML