Release 10.1A: OpenEdge Development:
AppBuilder

The message-handling relationship: internal details

The process for handling a message is very much the same regardless of whether the message is coming in or going out.

Outbound message and reply-handling process

Sending a message requires cooperation between the SmartProducer and an object serving as the OUTMESSAGE-SOURCE (OMS). Generally you would use either a SmartB2BObject or a SmartSender as OMS. Figure 6–10 illustrates the process.

Figure 6–10: Outbound message-handling process

The steps below describe the process.

When a message is to be sent, the OMS calls sendMessage in the SmartProducer.
The sendMessage() routine in the SmartProducer creates an empty message. It then calls sendHandler() in the OMS, passing the handle of the message it created.
The sendHandler() routine in the OMS sets the message header properties, adds a body to the message, and returns.
The sendMessage() routine in the SmartProducer now has a complete message to send and calls the relevant routines in the 4GL-JMS API to start the message on its way.
When a reply comes in, replyHandler() in the SmartProducer calls replyHandler() in the OMS, passing it the handle of the reply.
The replyHandler() routine in the OMS gets the ID of the original message and the reply properties and body. It performs any desired processing on that information and returns.

Inbound message-handling and reply process

Receiving a message requires cooperation between the SmartConsumer and an object serving as the INMESSAGE-TARGET (IMT). Generally you would use either a SmartB2BObject or a SmartReceiver as IMT. Figure 6–11 illustrates this process.

Figure 6–11: Inbound message-handling process

If you use a SmartRouter to distribute incoming messages, the SmartRouter acts as an IMT proxy, accepting calls from the SmartConsumer and passing them on transparently to the real IMT. The brief description below ignores the role of the SmartRouter:

When a message is received, the messageHandler() routine in the SmartConsumer calls the receiveHandler() routine in the IMT, passing the handle of the received message.
The receiveHandler() routine in the IMT extracts header properties and the message body, performs any desired processing, and returns.
If the message requires a reply, the messageHandler() routine in the SmartConsumer creates an empty reply message and calls sendReplyHandler() in the IMT, passing the handle of the reply it created.
The sendReplyHandler() routine in the IMT sets the header properties, adds a body, and returns.
The messageHandler() routine in the SmartConsumer now has a complete reply message to send and calls the relevant routines in the 4GL-JMS API to start it on its way.