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From "*Colin Sharples" <Colin.Sharp...@hbl.co.nz>
Subject RE: Workflow
Date Tue, 13 Nov 2001 22:15:54 GMT
Woohoo! That is exactly what I've been looking for. At the moment I've just
got my code running in a standalone process which kicks off threads to
handle the messages. I did want to have it running in a servlet engine, but
couldn't be bothered working out how to integrate the message listeners with
servlets. Your code seems to be exactly what I need.

Now, as far as integrating Messenger and Workflow, I have some code which
will probably do the job. It's fairly simple, and boils down to:

1. A mechanism for mapping activities to messages. This really just extends
Craig's Registry mechanism, so that for any given message using a
combination of the destination and/or message type allows you to identify
which activity to run on that message.

2. A mechanism for translating the contents of the message into the activity
context. I just defined an interface called ContextPopulator, with one
method:
  public Context populateContext(Message) throws JMSException;
When the activity definitions are being parsed and registered, you also
create a number of beans which implement ContextPopulator and associate them
with the relevant activities.

3. Something which implements onMessage() and does:
   - populate the context from the message
   - set the activity on the context
   - execute the activity
and also handles other stuff like exceptions (commit or rollback on the
queue session), checking for poisoned messages etc.

The last bit is the candidate for being a MessageDrivenObject. The servlet
can handle the registration of the activities and context populators. Hmm.
Okay, if I get some time I'll see if I can modify my stuff to use Messenger.


Colin. 

-----Original Message-----
From: James Strachan [mailto:james_strachan@yahoo.co.uk]
Sent: Wednesday, 14 November 2001 12:12 a.m.
To: Jakarta Commons Developers List
Subject: Re: Workflow


Hi Colin

----- Original Message -----
From: "*Colin Sharples" <Colin.Sharples@hbl.co.nz>
> BTW, I've been working on an implementation of the workflow system, which
> definitely rocks. I've created an execution environment based on JMS -
> activities are triggered by messages arriving on queues. I'm not sure what
> the attitude of the client I'm working for is, but I may be able to submit
> the generic JMS stuff I've been working on when I'm finished
(mid-December).

I'm working on a JMS framework called Messenger...

http://jakarta.apache.org/commons/messenger.html

... which provides a framework for working with JMS and dispatching JMS
messages to MessageListeners & Servlets & JSP. So, for example, JSP custom
tag libraries could be used to process JMS messages to perform XPath, XSLT
or SQL operations etc. It should be quite easy to integrate with the
existing commons-workflow project.

There could well be some crossover with what you are doing as well with the
workflow project. I'd be interested in any thoughts you might have on the
Messenger project and am interested to hear more of your JMS based workflow
system.

James


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