Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions (Addison-Wesley Signature Series (Fowler))

by Hohpe Gregor

Two applications sending requests and replies to each other are not very helpful. What is interesting is what the two messages represent. 1. Messaging RPC—This is how to implement Remote Procedure Invocation (50) using messaging. The request is a Command Message (145) that describes the function the replier should invoke. The reply is a Document Message (147) that contains the function’s return value or exception. 2. Messaging Query—This is how to perform a remote query using messaging. The request is a Command Message (145) containing the query, and the reply is the results of the query, perhaps a Message Sequence (170). 3. Notify/Acknowledge—This provides for event notification with acknowledgment, using messaging. The request is an Event Message (151) that provides notification, and the reply is a Document Message (147) acknowledging the notification. The acknowledgment may itself be another request, one seeking details about the event.