Message Router

Multiple processing steps in a Pipes and Filters chain are connected by Message Channels. A Message Channel decouples the sender and the receiver of a Message. This means that multiple applications can publish Messages to a Message Channel. As a result, a message channel can contain messages from different sources that may have to be treated differently based on the type of the message or other criteria. You could create a separate Message Channel for each message type (a concept explained in more detail later as a Datatype Channel) and connect each channel to the required processing steps for that message type. However, this would require the message
originators to be aware of the selection criteria for different processing steps, so that they can publish the message to the correct channel. It could also lead to an explosion of the number of Message Channels. Also, the decision on which steps the message undergoes may not just depend on the origin of the message. For example, we could imagine a situation where the destination of
a message changes by the number of messages that have passed through the channel so far. No single originator would know this number and would therefore be unable to send the message to the correct channel.

Insert a special filter, a Message Router, which consumes a Message from one Message Channel and republishes it to a different Message Channel channel depending on a set of conditions.