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

by Hohpe Gregor

none of the Selective Consumers on a channel match the message’s selector value, the message will be ignored as if the channel has no receivers. A similar problem in procedural programming is a case statement where none of the cases match the value being tested. Thus, a case statement can have a default case that matches values that aren’t matched by any other case. Applying this approach to messaging, it may seem tempting to create some sort of default consumer for messages that otherwise have no matching consumer. Yet, such a default consumer will not work as desired because it would require an expression that matches all selector values, so it would compete with all other consumers. Instead, to implement a default consumer, use a Message Dispatcher (508) that implements a case statement with a default option for unhandled cases that uses the default consumer.