HL7 inbound : recommended architecture?

Question

Hi,
What's the best way to process inbound HL7 messages?
Some details:
1. Inbound messages will all be ADT
2. There's a lot of common processing, for example the PID segment of every message type will be handled the same.
3. HL7 2.3.1, JCAPS 5.1.3
One suggestion is to first unmarshall to HL7_GENERIC_EVT then unmarshall to the specific event type (eg HL7_231_ADT_A01).
But how to do the common processing and keep maintainable code? The problem is the OTD object name is different for every message type. The only obvious solution requires code that is difficult to maintain like:
// Ugly code that is hard to maintain
If A01 then { A01.unmarshall(str); MSH = A01.getMSH(); PID = A01.getPID() ...}
If A02 then { A02.unmarshall(str); MSH = A02.getMSH(); PID = A02.getPID() ...}
If A03 then { A02.unmarshall(str); MSH = A03.getMSH(); PID = A03.getPID() ...}
etc.
Does anyone know if there is some superclass of the HL7 OTD's? If so it's possible to cast the OTD object up? Then for most segments this would work:
// Better.
if A01 then { A01.unmarshall(str); ADT = (Some SuperClass)A01 }
if A02 then { A02.unmarshall(str); ADT = (Some SuperClass)A02 }
MSH = ADT.getMSH()
PID = ADT.getPID()
Another way would be to dynamically create the object. I can get this to work, but only if the OTD is included in the collab properties, (which worries me). Also I cant find the constructor in the documents. Has anyone used this method?
// Probably the best
if A01 then ADT = new HL7_231_ADT_A01()
if A02 then ADT = new HL7_231_ADT_A02()
ADT.unmarshall(str);
MSH = ADT.getMSH()
PID = ADT.getPID()

Answer 1

We generally treat ADT as the "event" and create a generic OTD to match all event types. The downside is you need to make some segments optional which would actually be required for certain events. If the source system sends swap messages such as A17s, you also need to have a group of upto 2 PID, PV1s etc.