How do we route a message through multiple processing steps when the required steps may not be known at design-time and may not be sequential?
Use a central processing unit, a Process Manager, to maintain the state of the sequence and determine the next processing step based on intermediate results.
With Camel this pattern is implemented by using the Dynamic Router EIP. Camel’s implementation of the dynamic router maintains the state of the sequence, and allows to determine the next processing step based dynamically.
On the other hand the Routing Slip EIP demonstrates how a message can be routed through a dynamic series of processing steps. The solution of the Routing Slip is based on two key assumptions:
the sequence of processing steps has to be determined up-front
and the sequence is linear.
In many cases, these assumptions may not be fulfilled. For example, routing decisions might have to be made based on intermediate results. Or, the processing steps may not be sequential, but multiple steps might be executed in parallel.