The Change Of Address application is fundamentally a pub/sub application. As address changes are made in the postal service database via option 3 - “Add/Update Address”, notifications have to be made to all the interested parties. To achieve this end, we use WebSphere Message Broker’s pub/sub capabilities.
We want to mention the existence of the WebSphere MQ Publish/Subscribe facilities supplied as part of WebSphere MQ 5.3 fixpack 8 and above. We could certainly have used this facility as a pub/sub engine; however, WebSphere MQ Publish/Subscribe does not run on WMQ for z/OS. But apart from this, there is no technical reason we could not use the WebSphere MQ Publish/Subscribe broker by using another platform as the pub/sub engine.
It is straightforward to set up the pub/sub environment using the WMB Toolkit.
Create New Topic - Principle Definition
Next, we need to add a subscription into the subscription table for every client needing to be notified of the change of address. For our simple examples this is just a handful, but in reality this could be hundreds of clients. To add a subscription, WMB requires that we send a special format subscription message to a dedicated broker queue called SYSTEM.BROKER.CONTROL.QUEUE. The format of this message is described in the WMB Infocenter as follows:
The Register Subscriber command message is sent to a broker by a subscriber, or by another application on behalf of a subscriber, to indicate that it wants to subscribe to one or more topics at a subscription point. A message content filter can also be specified.
The Register Subscriber command message is an XML format message. For convenience and clarity, we use the PubSub support in the IH03 SupportPac™ - RFHUtil to create this message for us. (See the WMB Support site for a link to the supportPacs.)
RFHUtil can construct the necessary XML command message and place the message on the broker control queue for us, but we need to supply some details about our subscription:
The RFHUtil window looks similar to Figure.
Register a subscription with RFHUtil
Query Subscriptions in the broker toolkit
It is a now simple matter of adding new subscriptions as required using the RFHUtil. Now, we create a simple WMB message flow to perform the message publication. The UpdateAddress application in CICS writes a message to a WMQ queue called CICSWSAP.PUBLICATION.QUEUE. Our simple publication message flow needs to take this message and publish it in our topic. Next, we deal with creating this message flow in WMB.
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Service-oriented Architecture And Cics
Cics As A Service Provider And Requester
Modern Web Services Development Tools
Development Of The Change Of Address Cics Application
Exposing Our Application As A Web Service
Developing Web Service Clients
Tracing The Change Of Address Scenario
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