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From Ali Sadik Kumlali <as_kuml...@yahoo.com>
Subject [Axis2][1.1 Nightly] Why a JMS destination should be dedicated to only a single service (and vice-versa)?
Date Thu, 02 Nov 2006 09:43:41 GMT
Hi all,

Sorry for this long message :)

Nowadays, I'm trying to dispatch messages come through different destinations to a single
service.  However, current JMS implemantation enforces a one-to-one relationship between service
and the destination. Thus, the following operations is not allowed:
- A single destination can be used for messages of different services
- Multiple destinations can be used for messages of the same service

By looking at the implemantation, I've seen that is because of the difficulties of dispatching
when it comes to JMS. Destination-service relation is established in services.xml and dispatching
is done according to this relation. That is, when a JMS message comes in, service of the destination
is set to the MC and no dispatching is done for service discovery. Later, SOAPActionBasedDispatcher
is used to get the operation.

Actually, I feel that the transport and/or dispatching related definition should not be reside
in services.xml. And, I believe, this unique behaviour of JMS tranport is inconsistent with
the implementations of other transports. 

So, I've been searching a better way for dispatching JMS messages without that restriction.


When I look at more deeply, I see that RequestURIBasedDispatcher is not capable of dispatching
JMS messages, since we don't have "to" field in MC. If, somehow, we were able to pass JMS
URL to "to" field, RequestURIBasedDispatcher would not be sufficient to understand JMS URL.

Ok. What about SOAPActionBasedDispatcher? Can I use it for finding my service, based on the
SOAPAction? Nope. Because, it is not implemented yet. And I'm not sure how it would be possible
to discover the service from the SOAPAction. Iterate over the deployed services and lookup
the operation for each service? If yes, what would happen if two services had the same SOAPAction?
Choose the first matching one? :)

After RequestURIBasedDispatcher and SOAPActionBasedDispatcher is passed, I still don't have
either service or operation in MC. Then I enter the Security phase where I'm asked for service
name, and of course, a NPE is thrown :)

Does it make sense to enter AddressingBasedDispatcher before entering Security phase? Nope,
because of the same thing happens in RequestURIBasedDispatcher: I don't have "to" field in
MC.

OK. Can I use SOAPMessageBodyBasedDispatcher? Nope, because;
  - messageContext.getConfigurationContext().getServiceContextPath(): axis2/services
  - namespace of the first element(filePart): http://ws.mycompany.com/schemas/account_1_0
  - Utils.parseRequestURLForServiceAndOperation() returns no service and operation

Then, what would be the possible solution? 
- At sender side:
   - Adding service name to the JMS URL
   - Adding service name to the JMS message header before sending it (the same approach used
for transferring SOAPAction)
- At receiver side:
  - Setting "to" field of the MC to the value of service name field retrieved from JMS message
header.
  - Setting "soapAction" field of the MC to the value of SOAPAction field retrieved from JMS
message header (this is already done with the current implementation).
  - Letting SOAPActionBasedDispatcher to find the operation by using soapAction value in MC
(this is already done with the current implementation). 

All the transports send service name (and operation name) with the request, but JMS. Please
look at the following EPRs:
- HTTP: http://127.0.0.1:8080/axis2/services/EchoXMLService/echoOMElement
- SMTP: mail:foo@127.0.0.1/axis2/services/EchoXMLService/echoOMElement
- TCP: tcp://127.0.0.1:8080/axis2/services/EchoXMLService/echoOMElement
- JMS: jms:/destinationName?transport.jms.ConnectionFactoryJNDIName=conFactName&...

By sending service name with the JMS request, we would;
- be more consistent
- not need service-destination mapping in services.xml
- use a single destination for multiple services
- dispatch messages come from different destionations to the same service

Any thoughts?

Regards,

Ali Sadik Kumlali





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